Atanasio a cliffface opening in the Sierra de Jurez mountains of Oaxaca Mexico. The mountains are home to the Chev...
Atanasio, a cliff-face opening in the Sierra de Juárez mountains of Oaxaca, Mexico. The mountains are home to the Chevé system, some eighty-five hundred feet deep—potentially the deepest cave in the world.Photograph by Marcin Gala

On his thirteenth day underground, when he’d come to the edge of the known world and was preparing to pass beyond it, Marcin Gala placed a call to the surface. He’d travelled more than three miles through the earth by then, over stalagmites and boulder fields, cave-ins and vaulting galleries. He’d spidered down waterfalls, inched along crumbling ledges, and bellied through tunnels so tight that his back touched the roof with every breath. Now he stood at the shore of a small, dark pool under a dome of sulfurous flowstone. He felt the weight of the mountain above him—a mile of solid rock—and wondered if he’d ever find his way back again. It was his last chance to hear his wife and daughter’s voices before the cave swallowed him up.

“Base camp, base camp, base camp,” he said. “This is Camp Four. Over.” His voice travelled from the handset to a Teflon-coated wire that he had strung along the wall. It wound its way through sump and tunnel, up the stair-step passages of the Chevé system to a ragged cleft in a hillside seven thousand feet above sea level. There, in a cloud forest in the state of Oaxaca, Mexico, lay the staging area for an attempt to map the deepest cave in the world—a kind of Everest expedition turned upside down. Gala’s voice fell soft and muffled in the mountain’s belly, husky with fatigue. He asked his seven-year-old, Zuzia, how she liked the Pippi Longstocking book she’d been reading, and wondered what the weather was like on the surface. Then the voice of Bill Stone, the leader of the expedition, broke over the line. “We’re counting on you guys,” he said. “This is a big day. Do your best, but don’t do anything radical. Be brave, but not too brave.”

Gala had been this deep in the cave once before, in 2009, but never beyond the pool. A baby-faced Pole of unremarkable physique—more plumber than mountaineer—he discovered caving as a young man in the Tatra Mountains, when they were one of the few places he could escape the strictures of Communism. When he was seventeen, he and another caver became the first people to climb, from top to bottom, what was then the world’s deepest cave, the Réseau Jean Bernard, in the French Alps. Now thirty-eight, he had explored caves throughout Europe and Ukraine, Hawaii, Central America, and New Guinea. In the off-season, he was a technician on a Norwegian oil platform, dangling high above the North Sea to weld joints and replace rivets. He was not easily unnerved. Then again Chevé was more than usually unnerving.

Caves are like living organisms, James Tabor wrote in “Blind Descent,” a book on Bill Stone’s earlier expeditions. They have bloodstreams and respiratory systems, infections and infestations. They take in organic matter and digest it, flushing it slowly through their systems. Chevé feels more alive than most. Its tunnels lie along an uneasy fault line in the Sierra de Juárez mountains and seethe with more than seven feet of rain a year. On his first trip to Mexico, in 2001, Gala nearly died of histoplasmosis, a fungal infection acquired from the bat guano that lined the upper reaches of a nearby cave. The local villagers had learned to steer clear of such places. They told stories of a malignant spirit that wandered Chevé’s tunnels, its feet pointing backward as it walked. When Western cavers first discovered the system, in 1986, they found some delicate white bones beneath a stone slab near the entrance: the remains of children probably sacrificed there hundreds of years ago by the Cuicatec people.

When the call to base camp was over, Gala hiked to the edge of the pool with his partner, the British cave diver Phil Short, and they put on their scuba rebreathers, masks, and fins. They’d spent the past two days on a platform suspended above another sump, rebuilding their gear. Many of the parts had been cracked or contaminated on the way down, so the two men took their time, cleaning each piece and cannibalizing components from an extra kit, knowing that they’d soon have no time to spare. The water here was between fifty and sixty degrees—cold enough to chill you within minutes—and Gala had no idea where the pool would lead. It might offer swift passage to the next shaft or lead into an endless, mud-dimmed labyrinth.

“Half a dozen brown—three large, three jumbo!”

The rebreathers were good for four hours underwater, longer in a pinch. They removed carbon dioxide from a diver’s breath by passing it through cannisters of soda lime, then recirculating it back to the mouthpiece with a fresh puff of oxygen. Gala and Short were expert at managing dive time, but in the background another clock was always ticking. The team had arrived in February, three months before the rainy season. It was only mid-March now, but the weather wasn’t always predictable. In 2009, a flash flood had trapped two of Gala’s teammates in these tunnels for five days, unsure if the water would ever recede.

Gala had seen traces of its passage on the way down: old ropes shredded to fibre, phone lines stripped of insulation. When the heavy rain began to fall, it would flood this cave completely, trickling down from all over the mountain, gathering in ever-widening branches, dislodging boulders and carving new tunnels till it poured from the mountain into the Santo Domingo River. “You don’t want to be there when that happens,” Stone said. “There is no rescue, period.” To climb straight back to the surface, without stopping to rig ropes and phone wire, would take them four days. It took three days to get back from the moon.

The truth is they had nowhere better to go. All the pleasant places had already been found. The sunlit glades and secluded coves, phosphorescent lagoons and susurrating groves had been mapped and surveyed, extolled in guidebooks and posted with Latin names. To find something truly new on the planet, something no human had ever seen, you had to go deep underground or underwater. They were doing both.

Caving is both the oldest of pastimes and the most uncertain. It’s a game played in the dark on an invisible field. Until climbing gear was developed, in the late nineteenth century, a steep shaft could end an expedition, as could a flooded tunnel—cavers call them terminal sumps. If an entrance wasn’t too small or a tunnel too tight, the cave could be too deep to be searched by torch or candlelight. In the classic French caving books of the nineteen-thirties and forties, “Ten Years Under the Earth,” by Norbert Casteret, and “Subterranean Climbers,” by Pierre Chevalier, the expeditions are framed as manly jaunts belowground—a bit of stiff exercise before the lapin chasseur back at the inn. The men wear oilskins and duck-cloth trousers, carry rucksacks and rope ladders, and light their way with a horse-carriage lantern. At one point in “Subterranean Climbers,” a sweet scent of Chartreuse fills the air and the party realizes, with dismay, that their digestif has come to grief against a fissure wall. Later, a rock tumbles loose from a shaft and conks a caver named François on the head, causing some discomfort. The victim, Chevalier notes with regret, was “poorly protected by just an ordinary beret.”

Chevalier and his team went on to map more than ten miles of caverns in the Dent de Crolles, outside Grenoble. Along the way, they set the world depth record—twenty-one hundred and fifty-nine feet—and developed a number of caving tools still used today, including nylon ropes and mechanical ascenders. Casteret may have done even more to transform the sport. In the summer of 1922, he was hiking in the French Pyrenees when he noticed a small stream flowing from the base of a mountain. He shucked off his clothes and lit a candle, then wedged himself through the crack and waded in. The tunnel followed the stream for a couple of hundred feet, then dipped below the waterline. Rather than turn back, Casteret set his candle on a ledge, took a deep breath, and swam ahead, groping the wall till he felt the ceiling open up above him. He went on to explore many miles of tunnels inside the cave, culminating in a pair of large, airy galleries. The first was covered in spectacular limestone formations. The second was smaller and drier, with a dirt floor. When Casteret held his candle up to its walls, the flame flickered over engravings of mammoths, bison, hyenas, and other prehistoric beasts—the remains of a religious sanctuary some twenty thousand years old.

Casteret and Chevalier helped turn caving into a heroic undertaking, and the search for the world’s deepest cave into an international competition—a precursor to the space race. “Praise Heaven, no one can give France lessons in this matter of epic achievement,” Casteret wrote, in his preface to Chevalier’s book. “The race of explorers and adventure-seekers has not died out from our land.” By combining lighter, stronger climbing gear with scuba tanks, cavers went deeper and deeper into the earth, more than tripling Chevalier’s depth in the next sixty years. The record would bounce between France, Spain, and Austria (where one of Gala’s teams went below fifty-three hundred feet at Lamprechtsofen in 1998), before settling in the Republic of Georgia, in 2004.

A map of the Chevé system.

A cave’s depth is measured from the entrance down, no matter how high it is above sea level. When prospecting for deep systems, cavers start in mountains with thick layers of limestone deposited by ancient seas. Then they look for evidence of underground streams and for sinkholes—sometimes many miles square—where rain and runoff get funnelled into the rock. As the water seeps in, carbon dioxide that it has picked up from the soil and the atmosphere dissolves the calcium carbonate in the stone, bubbling through it like water through a sponge. In Georgia’s Krubera Cave, in the Western Caucasus, great chimneylike shafts plunge as much as five hundred feet at a time, with crawl spaces and flooded tunnels between them. The current depth record was set there in 2012, when a Ukrainian caver named Gennadiy Samokhin descended more than seventy-two hundred feet from the entrance—close to a mile and a half underground.

The Chevé system is even deeper. Drop some fluorescent dye into the stream at the entrance, as a teammate of Stone’s did in 1990, and it will tumble into the Santo Domingo eight days later, eleven miles away and eighty-five hundred feet below. No other cave in the world has such proven depth (though geologists suspect that some caves in China, New Guinea, and Turkey go even deeper). But that isn’t enough to set a record: cave depths, unlike mountain heights, are inherently subjective. Everest was the world’s tallest peak long before Edmund Hillary and Tenzing Norgay scaled it. But a cave is only officially a cave when people have passed through it. Until then, it’s just another hole in the ground.

Deep caves rarely call attention to themselves. Like speakeasies and opium dens, they tend to hide behind shabby entrances. A muddy rift will widen into a shaft, a crawl space into a vaulting nave. Krubera begins as a grave-size hole full of moss and crows’ nests. When local cavers first explored it, in 1960, they got less than three hundred feet down before the shaft levelled off into an impassable squeeze. It was more than twenty years before the passage was dug out, and another seventeen before a side passage revealed the vast cave system beneath it. Yet the signs were there all along. The bigger the cave, the more air goes through it, and Krubera was like a wind tunnel in places. “If it blows, it goes,” cavers say.

Chevé has what cavers call a Hollywood entrance: a gaping maw in the face of a cliff, like King Kong’s lair on Skull Island. A long golden meadow leads up to it, bordered by rows of pines and a stream that murmurs in from the right. It feels ceremonial somehow, like the approach to an altar. As you walk beneath the overhang, the temperature drops, and a musty, fungal scent drifts up from the cave’s throat, where the children’s bones were found. The stream passes between piles of rubble and boulders, their shadows thrown into looming relief by your headlamp. Then the walls close in and the wind begins to rise. It’s easy to see why the Cuicatec felt that some dark presence abided here—that something in this place needed to be appeased.

Like Krubera, Chevé starts with a precipitous drop: three thousand feet in less than half a mile. But then it levels off to a more gradual slope: to go another vertical mile, you have to go ten miles horizontally, at least half a mile of it underwater. Although the water eventually gathers into a single stream, the cave’s upper reaches are full of oxbows and tributaries, meandering and intertwining through the rock, paralleling one another for a stretch, then veering apart or abruptly ending. It’s tempting to imagine the system as a giant Habitrail, with cavers scurrying through it. But these tunnels weren’t meant for inhabitants. They’re geological formations, differentially eroded, their soft deposits ground down to serrated edges or carved into knobs and spikes that the body has to contort itself around. A long squirm down a tight shaft will lead to an even longer crawl, a slippery descent, and so on, in a natural obstacle course, relentless in its challenges. Near the main entrance, there’s a thirty-foot section known as the Cat Walk, where a caver can hoist his pack and stroll forward without thinking. It’s the only place like it in the system. “Every other piece of this cave might kill you,” Gala told me.

Bill Stone has led seven expeditions to Chevé in the past ten years, all but one of them with Gala. In 2003, his team dove through a sump that had thwarted cavers for more than a decade, then climbed down to nearly five thousand feet, making Chevé the deepest cave in the Western Hemisphere. But there was no clear way forward: the main passage ended in a wall of boulders. The only option was to try to bypass the blockage by entering the system farther downslope. The following spring, Stone sent teams of Polish, Spanish, Australian, and American cavers bushwhacking across the cloud forest in search of new entrances. They found more than a hundred, including a spectacular cliff-face opening called Atanasio. The most promising, though, was a more modest but gusty opening labelled J2 (the “J” was for jaskinia—Polish for “cave”). It was wide open at the top, but pinched tight as soon as you went down. The Australians called it Barbie.

“As far as I know, is the only job he’s created.”

The J2 system runs roughly parallel to the main Chevé passage and about a thousand feet above it. The water’s exact course through the mountain is hard to predict, but cave surveys and Stone’s 3-D models suggest that the two systems eventually merge. If Gala and Short could get past the sump beyond Camp Four, their route should join up with Chevé, drop another twenty-five hundred feet, and barrel down to the Santo Domingo. “Imagine a storm-tunnel system in a city,” Stone told me. “All these feeders connect to a trunk and then go out to an estuary. We’re in the back door trying to get into that primary conduit.” This is it, he said. This is the big one. “If everything goes well, we’ll be as far as anyone has ever been inside the earth.”

Deep caving demands what Stone calls siege logistics. It’s not so much a matter of conquering a cave as outlasting it. Just to set up base camp in Mexico, his team had to move six truckloads of material more than twelve hundred miles and up a mountain. Then the real work began. Exploring Chevé is like drilling a very deep hole. It can’t be done in one pass. You have to go down a certain distance, return to the surface, then drill down a little farther, over and over, until you can go no deeper. While one group is recovering on the surface, the other is shuttling provisions farther into the cave. Stone’s team had to establish four camps underground, each about a day’s hike apart. Latrines had to be dug, ropes rigged, supplies consumed, and refuse carried back to the surface. Divers like Gala and Short were just advance scouts for the mud-spattered army behind them, lugging thirty-pound rubber duffelbags through the cave—sherpas of a sort, though they’d never set foot on a mountaintop. Stone called them mules.

Two months earlier, in Texas, I’d watched the final preparations for the trip. Stone’s headquarters are about fifteen minutes southeast of Austin, on thirty acres of drought-stricken scrub. There is a corrugated building out front that’s home to Stone Aerospace, a robotics firm he started in 1998, and a two-story log house in back, where he lives with his wife, Vickie, a fellow-caver. (They met at a party where Stone overheard her talking about tactical rigging.) The trucks were scheduled to leave in two days, and every corner of the house had been requisitioned for supplies. One room was piled with cook pots, cable ladders, nylon line, and long underwear. Another had dry suits, diving masks, rebreathers, and oxygen bottles. In the basement, eight long picnic tables were stacked with more than a thousand pounds of provisions. Shrink-wrapped flats of peanuts, cashews, and energy bars sat next to rows of four-litre bottles filled with staples and dry mixes: quinoa, oatmeal, whey protein, mangos, powdered potatoes, and broccoli-cheese soup. Stone had tamped in some of the ingredients using an axe handle.

“In the past, I’d lose twenty-five pounds on one of these trips,” Stone told me. “We can burn as many calories as a Tour de France rider every day underground.” Ascending Chevé, he once said, was like climbing Yosemite’s El Capitan at night through a freezing waterfall. To fine-tune the team’s diet, he’d modelled it on Lance Armstrong’s program, aiming for a ratio of seventeen per cent protein, sixteen per cent fat, and sixty-seven per cent carbohydrates. In Mexico, the supplies would be replenished with local beans, vegetables, and dried machaca beef. “What you aren’t going to find is candy,” Stone said. “Stuff like Snickers—that’s bullshit.” When I looked closer, though, I found a bottle of miniature chocolates that Vickie had hidden among the supplies.

Cavers, even more than climbers, have to travel light and tight. Bulky packs are a torture to get through narrow fissures, and every ounce is extracted tenfold in sweat. Over the years, caving gear has undergone a brutal Darwinian selection, lopping off redundant parts and vestigial limbs. Toothbrushes have lost their handles, forks a tine or two, packs their adjustable straps. Underwear is worn for weeks on end, the bacteria kept back by antibiotic silver and copper threads. Simple items are often best: Nalgene bottles, waterproof and unbreakable, have replaced all manner of fancier containers; cavers even stuff their sleeping bags into them. Yet the biggest weight savings have come from more sophisticated gear. Stone has a Ph.D. in structural engineering from the University of Texas and spent twenty-four years at the National Institute of Standards and Technology, in Gaithersburg, Maryland. His company has worked on numerous robotics projects for NASA, including autonomous submarines destined for Europa, Jupiter’s sixth moon. The rebreathers for the Chevé trip were of his own design. Their carbon-fibre tanks weighed a fourth of what conventional tanks weigh and lasted more than four times longer underwater; their software could precisely regulate the mix and flow of gases.

Bill Stone has led several trips to Chevé. “We can burn as many calories as a Tour de France rider every day underground,” he says.

Photograph by Emiliano Granado

Stone’s newest obsession was a set of methanol fuel cells from a company called SFC Energy. Headlamps, phones, scuba computers, and hammer drills (used to drive rope anchors into the rock) all use lithium batteries that have to be recharged. On this trip the cavers would also be carrying GoPro video cameras for a documentary that would be shown on the Discovery Channel. In the past, Stone had tried installing a paddle wheel underground to generate electricity from the stream flow, with fairly feeble results. But a single bottle of methanol and four fuel cells—each about the size of a large toaster—could power the whole expedition. The question was whether they’d survive. High-tech gear tends to be fragile and finicky. While I was in Texas, one of the rebreathers kept shutting down for no apparent reason (it was later found to have a faulty fail-safe program), and this was the sixth generation of that design. The fuel cells weren’t nearly as robust. Stone would keep them in shockproof, watertight cases, but he doubted that would suffice. “We’re going to take them down there and turn them into broken pieces of plastic,” he said.

Stone knew what it meant to be a battered piece of hardware: he’d turned sixty that December and had spent more than a year of his life underground. His gangly frame—six feet four, with a wingspan nearly as wide—was kept knotty by free weights, and he could still outclimb and outcarry most twenty-five-year-olds. But he was getting old for an extreme sport like this, and he knew it. He had the whiskered, weather-beaten look of an old lobsterman. “I think it’s a little surprising to him how hard the caving is on his body these days,” one of the team members told me. “I won’t say that he’s feeling his age, but he’s realizing that he isn’t at the pointy end of the stick anymore.”

As a leader, Stone models himself on the great expeditionary Brits of the past century. He has an engineer’s methodical mind and an explorer’s heroic self-image. He’s pragmatic about details and romantic about goals. His teammates often compare him to Ernest Shackleton, another explorer who felt most alive in the world’s most unpleasant places. But Shackleton, despite shipwreck and starvation, never lost a man under his direct command. (“I thought you’d rather have a live donkey than a dead lion,” he told his wife, after failing to reach the South Pole.) Cave diving is less forgiving. Stone has lost four teammates on his expeditions, including Henry Kendall, the Nobel Prize-winning physicist. Kendall failed to turn on the oxygen in his rebreather while cave diving in Florida. Others have succumbed to narcosis or hypoxia, fallen from cliffs or had grand-mal seizures, lost their way or lost track of time. They’ve buried themselves so deep that they couldn’t come back up.

Stone’s single-minded, almost mechanistic style can sometimes raise hackles. He can be inspiring one moment and dismissive the next. “Bill has problems identifying people’s emotions,” Gala told me. “So he doesn’t always react to them well.” Then again it’s hard to avoid tension in a sport that takes such a mortal toll. Stone’s mentor, the legendary cave diver Sheck Exley, retrieved forty corpses from diving sites in Florida alone, then drowned in a Mexican cenote in 1994. “When cavers become cave divers, they usually die because of it,” Stone’s friend James Brown told me. In 1988, Brown and Stone were called in to help remove the body of a female diver from a cave near Altoona, Pennsylvania. When they found her, she was tangled in rope at the bottom of a sump, arms so stiff that, Brown recalled, Stone suggested they cut them off for easier transport. “Nobody liked that idea much,” Brown said. “But after a while her arms softened up, and we were able to fold them down.”

It took them two days to get her out, with Stone pushing from behind. “He kept saying, ‘Don’t leave me back here if she gets stuck!’ ” Brown said. If there’s one rule of caving, Stone told me, it’s that you never leave a person behind. Especially if they’re alive, he added. “If they’re dead, it’s another matter.”

By the time I arrived at base camp, in mid-March, the team had settled into a soggy routine. A week underground followed by ten days on the surface. Five days of drizzle followed by one day of sun. They’d spent most of the first month hauling gear up the mountain—a muddy three-hour hike from a farmhouse in the valley—loading the heaviest items on burros and the rest on their backs. They’d set up tents and dug latrines, strung lights and cut trails to the cave. The camp was spread out beneath pines and low-hanging clouds, on a rare stretch of relatively flat ground. To one side, the Discovery crew had erected a geodesic dome with two full editing stations inside. To the other, the cavers had hung a giant blue tarp, sheltering a long plywood table, stacks of provisions, and a pair of two-burner camp stoves. On most expeditions, base camp is a place to dry out and recover from infections acquired underground—cracked skin and inflamed cuts and staph bacteria that burrow under your fingernails till they ooze pus. But this forest was nearly as wet as the cave.

“Get another cab, Dad. This one is creepin’ me out.”

“Welcome to Hell,” one of the cavers told me, when I joined him by the campfire that first night. “Where happiness goes to die,” another added. There was a pause, then someone launched into the colonel’s monologue from “Avatar”: “Out there, beyond that fence, every living thing that crawls, flies, or squats in the mud wants to kill you and eat your eyes for jujubes. . . . If you wish to survive, you need to cultivate a strong mental attitude.” It was a favorite conceit around camp: the cloud forest as hostile planet. But, looking at all the gleaming eyes around the fire, I was mostly reminded of the Island of Lost Boys. Beneath all the mud and gloom and dire admonitions, there burned an ember of self-satisfaction—of pride in their wretched circumstance and willingness to endure it. As Gala put it, “It’s just one continuous miserable.”

Fifty-four cavers from thirteen countries, forty-three of them men and eleven women, would pass through the camp that spring. The team had a core of twenty or so veteran members, reinforced by recruits from caving groups worldwide. On any given day, the cave might be home to a particle physicist from Berkeley, a molecular biologist from Russia, a spacecraft engineer from Washington, D.C., a rancher from Mexico, a geologist from Sweden, a tree surgeon from Colorado, a mathematician from Slovenia, a theatre director from Poland, and a cave guide from Canada who lived in a Jeep and spent two hundred days a year underground. They were a paradoxical breed: restlessly active yet fond of tight places, highly analytical yet indifferent to risk. They seemed built for solitude—pale, phlegmatic creatures drawn to deep holes and dark passages—yet they worked together as a selfless unit: the naked mole rats of extreme sport. As far as I could tell, only two things truly connected them: a love of the unknown and a tolerance for pain.

Matt Covington, a thirty-three-year-old caver from Fayetteville, was a typical specimen. A professor of geology at the University of Arkansas, he had earned his Ph.D. in astrophysics but switched fields so that he could spend more time underground. He had a build best described as Flat Stanley. Six feet four but only a hundred and fifty pounds, he could squeeze through a crevice six and a half inches wide. “My head isn’t the limiting factor,” he told me. “It’s my hips.” Covington was a veteran of seven Stone expeditions as well as caving trips to Sumatra, Peru, and other remote formations. Five years earlier, he was climbing up a cliff face in Lechuguilla Cave, near Carlsbad Caverns, when an anchor came loose from the rock. Covington’s feet caught on the cliff as he fell, tumbling him onto his left arm, causing compound fractures. Rather than wait for rescue, he spent the next thirteen hours dragging himself to the surface. “The crawling was fairly uncomfortable,” he allowed. “There was a lot of rope to climb.”

When I first met Covington, late one night, he’d just slouched back into camp after five days underground. His eyes were bloodshot, his blond hair clumped and matted, his skin as blanched and fuzzy as moldy yogurt. He was so tired that he could barely stand, and his clothes reeked of cave funk. Yet he seemed fairly content. “A good caver is one who forgets how bad it really is,” he said. There was more to it than that, though. Covington didn’t feel claustrophobic underground; he felt at home. The rock walls, to him, offered a kind of embrace. As a boy, he told me, he used to flop around so much in his sleep that he often fell on the floor. Rather than climb back up, he’d crawl under the bed and stay till morning. He felt better there, beneath the springs, than he did looking up at the ceiling in his big empty room.

It was an instinct almost everyone here seemed to share. One of the cavers remembered staring at a slice of rye bread as a child, fascinated by all the air bubbles beneath the crust. He wanted to go down there. Gala was so comfortable in caves that he sometimes felt as if they were made for humans. “The passages are exactly the right size for my body to fit in,” he told me. And his wife, Kasia, who worked as a photo editor in Warsaw, was nearly as happy underground as he. They took turns exploring the cave and taking care of their daughter, Zuzia, up on the surface. Zuzia had spent much of her life watching people disappear into holes and reëmerge weeks later. She traversed her first cliff face at the age of four, in Spain’s Picos de Europa mountains, and kept a map above her bed with pirate flags pinned on all the countries she’d visited. When she first came to Mexico, in 2009, she would sometimes cry out in frustration, “It’s so uncomfortable here!” Now she flitted between tents like a forest sprite, half naked in the cold, fencing with corncobs and setting traps for mice. Life at camp had built up her immune system, Gala assured me, and had taught her the “skills of dynamic risk assessment.”

I wished that I could see Chevé through her eyes. Before her father went underground with Phil Short, for their long hike beyond Camp Four, he’d read to Zuzia from “The Hobbit.” Chevé was no Lonely Mountain. Yet it had glistening caverns and plummeting boreholes, stalagmites tall as organ pipes and great galleries draped in flowstone, deeper than any goblin lair. And they were right beneath her feet. “When you squeeze through these small holes into these big halls, you feel like you’re the only person on the earth,” Gala said. “It’s like the kingdom of the dwarves.”

A caver rappels down a waterfall.

Photograph by Kasia Biernacka

Gala had been exploring Chevé with Stone so long that he could nearly navigate it blindfolded. After a while, he said, you start to create a map of the system in your mind, to memorize each contortion and foothold needed to climb through a passage. On the steepest pitches, certain rocks almost seemed to smile and wave at him, and to reach for his hand. He would grab them, thinking, Old friend! And yet the deeper he went the more unfamiliar the territory became. By the thirteenth day, the escalating uncertainty—the risk of a careless stumble or a snapped limb so far from the surface—was starting to weigh on him. “The further in you go, the more you begin to doubt and question yourself,” he told me. “What the fuck am I doing here?”

The sump beyond Camp Four was like nothing Short and Gala had seen before. The three sumps higher up in this system were relatively shallow and less than five hundred feet long. This sump was more than thirty feet deep, and it seemed to go on and on. And something more rare: it was beautiful. The water was a luminous turquoise, flowing over pure-white sand; the limestone was streaked with ochre and rust. Most sumps are cloudy, tubelike passages carved by underground streams, but this one had been a dry cave not long ago. The stalactites on its ceiling could only have been formed by slow drip. With its lofty chambers and limpid water, it reminded Gala of the blue holes of Florida and the caves of the Yucatán. Finning through it felt like flying.

The hazards of cave diving are inseparable from its seductions. Wide-open tunnels can fork into a maze; white sands swirl up to obscure your view. You think that you know the way back only to reach a dead end, with no place to come up for air. “People think that cave diving is an adrenaline sport, but really it’s the opposite,” Short told me. “Whenever you feel your adrenaline racing, you have to slow down. Stop, breathe, think, act, and, in general, abort. That’s the rule in cave diving.”

Short is one of the sport’s premier practitioners, with experience as far afield as the Sahara and shipwrecks off Guam. His body is a testament to its rigors: long and arachnid, skin taut over bone, head shaved to shed its last encumbrance. With his rapid-fire talk and glasses that seem to magnify his eyes, he could pass for a street preacher or a pamphleteer. But his absurdist wit was a great gift around a campfire, and his diplomacy often took the edge off Stone’s blunt directives. Gala and Short were a good match: one quiet, the other loquacious; one expert at climbing, the other at diving. Just as Gala could pick his way through Chevé by memory and internal gyroscope, Short could divine a sump’s path from half-conscious clues: the flow of current and its fluctuating temperature, the shape of the walls and ripples in the sand. Still, he took no chances. As they swam from chamber to chamber, the beams of their headlamps needling the dark, he unspooled a three-millimetre line behind him, like Theseus in the Labyrinth.

An hour later, he signalled for Gala to stop. Below them in the sand was the line they’d laid down fifteen minutes earlier. The tunnel had led them on a loop. They’d expected the sump to be about a thousand feet long, but they’d already gone twice that distance, and time was running out. Cave divers like to ration their air supply by a rule of thirds: one part for the way in, another for the way out, and a third in reserve. On a four-hour rebreather, that left them less than half an hour for exploring. The cave was a honeycomb, they realized, with tunnels angling off in every direction and hardly any current to guide them. “There were passages everywhere, everywhere,” Gala recalled. “It was so complex we could spend a year looking.”

In the end, they just picked a tunnel and hoped for the best. When they’d backtracked around the loop, reeling in their line, they came to a kind of four-way intersection. One passage led back to the beginning of the sump, another to the loop behind them, a third to a dead end they’d explored earlier. That left one unexplored passage. It took them up a short corridor, along a rising slope of terraced mustard-colored flowstone, and into a small domed chamber. There was an air bell at the top about the size of a car trunk, so they swam up and took off their helmets and neoprene hoods to talk. They seemed to be at a dead end. They were cold, tired, and disoriented, and their air ration had nearly run out. There was no choice but to head back. “We were just a little overwhelmed by this dive,” Gala told me. Then they heard the waterfall.

A mile above them, at base camp, Stone was waiting impatiently for their call. This was the pivotal moment in the expedition—the day for which he’d spent four years perfecting gear, recruiting cavers, and raising money. (The total budget for the trip was roughly three hundred and fifty thousand dollars, most of it paid for by equipment sponsors and the Discovery Channel.) He had expected Gala and Short’s reconnaissance trip to take less than six hours—two hours to dive the sump, two hours to look around and find a camp site, and another two to swim back and call in—yet nine hours had passed. “There are a bunch of scenarios that could be going on right now,” he told the Discovery cinematographer, Zachary Fink. “Even a one-kilometre swim with fins would take only about an hour. And that was way beyond our limit.”

Matt Covington, a caver from Arkansas, who says that “a good caver is one who forgets how bad it really is.”

Photograph by Marcin Gala

Stone looked haggard and thin, his mustache drooping over sallow skin. Weeks of shuttling supplies into the cave had taken a toll on him. He was a strong climber and diver, but he wasn’t a “squeeze freak” like some of the others. His broad, bony shoulders weren’t built for these tunnels. In the tightest fissures he had to take off his helmet just to turn his head, or strip down to his dry suit and wriggle between walls for hundreds of feet. (They called one passage the Contusion Tubes.) “It’s hypothermic as hell down there,” he told me. “The wind is whipping through, the water’s in contact with the rock, and you can just feel the calories being sucked out. It can be more dangerous than a high-altitude peak at twenty-five below.” By the time he’d resurfaced a few days earlier, he was coming down with a flu. Then it rained for three and a half days.

It was late evening when the call finally came: “Base camp, base camp, base camp!” Stone rushed over to the phone and hit the talk button. “Tell us what happened,” he said. There was a blast of static, then Short’s clipped British accent came crackling over the line. “We have good news and we have complicated news,” he said. “From a point of view of future exploration, complicated is today’s understatement.”

The waterfall could mean only one thing, Short and Gala knew. They’d reached the end of the sump and the river was flowing nearby. How to get there? When Gala ducked his head underwater and looked around, the chamber looked sealed off. But when he looked again his headlamp picked up an odd texture in the wall to his right. There was a gap in it just below the waterline—wide enough for a person to squeeze through. Gala could tell that his rebreather wouldn’t fit, so he handed it to Short, along with his mask, helmet, and side tanks. “I left him holding all these things with his teeth and both his hands,” he recalled later. Then he held his breath and dove through.

When he resurfaced on the other side, he was in a fast-flowing canal of clear water. The walls were formed by ancient breakdown piles, their boulders napped in calcite; the low ceiling was hung with stalactites. As he swam, a wide, airy passage opened up ahead, with a large pool in the distance. It glimmered in his headlight. He hiked over to it and swam across, feeling light and buoyant without his rebreather. He could hear the roar of the waterfall growing louder as he went, but an enormous stalagmite blocked the way, with only a thin gap to one side. He stretched an arm and a leg through the opening and shimmied around, thankful again to be rid of his gear. When he was through, he found himself in a great chamber filled with mist and spray, its floor split by a yawning chasm. The river ran into it from the right and fell farther than his light could follow. Across the chamber, thirty or forty feet away, a huge borehole stretched into the darkness. This is it, Gala thought, the breakthrough they’d imagined. With any luck, it would take them straight to Chevé’s main passage.

Stone wasn’t so sure. “Is there any place at all over there that you saw that would be suitable for a camp?” he asked Short over the phone, when the story was done. “Negative. There is not a single flat surface other than the surface of the river.” Stone clutched his head and frowned. The sump was too long. Two thousand feet! They didn’t have enough line down there to rig that distance. Without rigging, most of the team couldn’t dive the sump safely, and without their help Gala and Short couldn’t resupply for the next push. “The whole game had changed,” Stone told me later. “Just diving through wasn’t the game. The game was to get all the support material to the other side. It was like running a war: if you don’t get the food and fuel and ammo to the front line, you’re going to stall out.”

Only a few dozen people in the world had both the caving expertise and the scuba skills to go this deep in the cave. Of those, twelve had originally agreed to join the expedition. Then the number began to drop. Three died before the expedition began: one on a deep dive in Ireland, another in an underwater crevice in Australia, the third from carbon monoxide poisoning in Cozumel. Three had left early or had not yet arrived. And three had physical limitations: James Brown had gimpy knees, a Mexican diver named Nico Escamilla had a pulled groin muscle, and a veteran diver named Tom Morris had torn a rotator cuff. “It was like getting hit in the head with a two-by-four,” Stone told me. “Oh, crap! We’ve lost most of our divers! The three that are qualified to dive the sump are the two that are down there and me—and, God bless them, Phil and Marcin want to see daylight.”

Marcin Gala, a Polish veteran, who climbed the deepest cave system then known, in the French Alps, when he was seventeen.

Photograph by Kasia Biernacka

It was too late to recruit new divers to the team. The best candidate, a veteran British caver named Jason Mallinson, had joined another expedition, across the river at a cave system called Huautla. “He’s one of the best divers in the world,” Stone told me. “But he has a certain personality—it’s abrasive, and what I really wanted this year was harmony, and I got it.” Stone had planned to join Gala and Short for the last leg of the expedition, to see the very deepest regions of the cave. But without more divers to support them he wasn’t sure it was safe to continue. “They did a fantastic thing there, but it may also be the end of that route,” he said, after Short got off the line. “There is no glory in rushing into something like that and losing a friend. It just is not worth it.”

Word of Stone’s misgivings filtered down to Gala and Short as they worked their way back up the cave, camping with the support crews. It seemed a kind of betrayal. The yo-yo logistics of deep caving required that they return to the surface to rest and reprovision, but they had every intention of going back down. Yes, the sump was longer than expected, the conditions more challenging. But they’d found exactly what they wanted on the other side. How could they stop now?

“My thinking was that Bill is just tired with this cave—that this is just an excuse not to come back,” Gala told me. “I think that he spent too much time preparing this expedition, making all these tools, all these deals.” But Stone insists that his reluctance was just a matter of safety and logistics—an equation like any other, balancing risk and reward. On Gala and Short’s first evening back at base camp, the scene around the campfire got so tense that Stone shouted at Zachary Fink to turn off his camera. “It’s always like that at some point in an expedition,” Gala told me. “There’s always a shouting match between Bill and me, with someone almost crying.” But over bourbon that night and coffee the next morning, they slowly hashed out a plan. They would have to work fast, resupplying the camps themselves and exploring the new tunnels without backup divers. If they hung hammocks from the wall beyond Sump Four, they could bivouac there and explore the cave for another three weeks before they ran out of rope. With any luck, they’d reach the Chevé juncture before they were done.

Stone went underground the next day. Short took five days to rest and heal—half the usual recovery time, after three times the usual stay underground—and by the morning of March 21st he was leading a ragtag team down the mountain. This was just a five-day trip to help prepare the cave for the final push. But with the expedition so undermanned, Short had no choice but to lead the team and to bring two novices along: Patrick van den Berg, a hulking information-security specialist from Holland, and David Rickel, an emergency medical technician from Texas. Van den Berg was a weekend caver in relatively poor shape (“I get most of my exercise moving a mouse around,” he told me). Rickel was the team medic. He had a rock climber’s ropy build, but the closest he’d come to deep caving was working in an iron-ore mine in Australia.

Short was of two minds about taking them. He knew that one injury could derail the whole expedition, and that the cave ahead would test even the fittest athlete. “You can lift weights and go wall climbing and run a few miles every day, but it’s not the same,” he told me, as we wound our way down the slope. “When you’re nineteen days underground, in the cold and wet without a bed, with a forty-pound pack on your back, crawling on your hands and knees or climbing up and down cliffs or diving through sumps, and then you come back and resurface, and four days into your ten-day break some sadist wants to send you back down under, and you end up volunteering to go—most people hear that and they think you’re stark raving mad.” Yet Short was an optimist at heart and an experienced teacher—he gave scuba and cave-diving lessons in England—and he’d seen even novices accomplish unimaginable things. “It’s not the body that breaks, it’s the mind,” he said. “If you compare this to what the British infantry were lugging in the Ardennes in World War I, or what Shackleton’s team did in the Antarctic, this shit is easy. They were trudging up those slopes with old-fashioned ropes and no oxygen, and I’m sitting here complaining about the hole in my antibacterial underwear.”

Whether van den Berg took any comfort in this wasn’t clear. Less than an hour from camp, he was already red-faced and wheezing, sweat streaming down his chest. The altitude was getting to him, he told me. Hiking at seven thousand feet made him feel like he was breathing through a straw. When the team set down its packs for a brief rest, Short came over and crouched beside him. “I’m a little concerned that you’re as tired as you are after just walking down a hill,” he told him. “Your pulse was up to one-sixty, which David tells me is pretty high.” Van den Berg shook his head and insisted that he was fine. He wouldn’t have a problem going down the cave. “But you have to come back out, too,” Short told him.

“All right, so I missed your soccer game. But didn’t my assistant send you a lovely fruit basket?”

We were headed toward a cave entrance known as the Last Bash, about a mile from base camp. Discovered in 2005, it was a side entrance to the J2 passage, an hour or so down the slope from the original entrance. It would allow the team to bypass a sump and cut twelve hours out of the trip down, but it was tighter and more punishing than the other entrance—just a crack in the rock ten feet above the trail, flanked by boulders and elephant-ear vines. If Short hadn’t pointed it out, I would have passed right by it.

Short’s team peered up at the opening for a moment, then slowly put on their gear. They stepped into their waterproof caving suits and climbing harnesses, attached special ratchets for rappelling down cliffs, and strapped on their helmets and headlamps. “This is not going to be some macho-driven bullshit,” Short assured them. “It’s going to be a slow bumble down the cave, with double dinners when we get to camp.” They made a quick snack of crackers and energy bars, while Rickel checked van den Berg’s heart rate again. It had dropped to a hundred and twenty. “How did you end up here?” van den Berg asked him when he’d finished. Rickel laughed. “A long sequence of poor life choices,” he said. Then they crawled into the crack one by one and disappeared.

The rains were getting to be a serious concern now. The tunnels below the Last Bash weren’t known to flood, but neither were the tunnels above it before 2009. Then some gravel got clogged in a fissure at the bottom of a pool, flooding the chamber behind it and trapping seven people in the cave below. Five were able to dive out, but the other two, Nikki Green and David Ochel, had to sit and wait, not knowing if the tunnel would clear. “We had no food for five days, just watching the water,” Green told me. In the end, the rain abated long enough for them to climb out, and then the cave flooded for the rest of the season. “We stayed too long,” Green said.

A neighboring cave, known as Charco, had an even more unpleasant history. In 2001, a team of six cavers was heading back to the surface there, after a week of surveying, when they noticed the underground stream starting to rise. It had been raining for two days by then, and the tunnel was so tight that it began to flood. Charco is a place to make even cavers claustrophobic: the first camp is a twelve-hour crawl from the surface, mostly on your belly. By the time the last team member neared the entrance, the water in the tunnel was inches from the ceiling. As he treaded water, lifting his face up to breathe, bits of soft white debris drifted toward his mouth and got caught in his hair. But it wasn’t debris, as it turned out. A cow had died in the entrance that spring. Its belly was infested with maggots and the rains had washed them into the cave.

If there was an advantage to going deep, it was that the cave was fairly sterile. In the lower reaches of J2, the only signs of life were a few translucent crustaceans and bits of refuse that washed down from above. (In the Huautla system, teams sometimes found Popsicle sticks a mile belowground.) By early April, the camps were reprovisioned, Rickel and van den Berg were safely back on the surface with Stone, and Gala and Short were alone once again at Camp Four. The sump beyond it, once the dark side of the moon, now seemed comfortingly familiar. Short had discovered a larger opening in the chamber at the end, which allowed them to dive out with their rebreathers and equipment. When they had swum down the canal on the other side and followed the tunnel to the misty chamber with the waterfall, it was as if they’d arrived at another beginning. “Now we were in truly dry, unexplored cave,” Short told me. “Our lights were the first light that had fallen on this place since it had been created.”

Two promising passages lay ahead: the fossil gallery where the river had once flowed, and the canyonlike fissure where it now fell. They took a moment to gather themselves at the top of the falls and to make a pot of hot chocolate. But Gala couldn’t bear to wait. While Short tended the stove, he free-climbed the forty feet to the other side of the canyon—ropes would come later. Then he shouted at Short to join him.

It was just as they’d hoped: a cavernous passage, perhaps fifteen feet high by thirty feet wide, with a packed mud floor. There was even a flat spot ahead where they could set up a camp. The gallery followed the path of the tunnel behind them at first, then meandered left and right, up and down. Gala and Short took surveyor’s notes as they went, one man walking ahead and holding up a saucepan lid while the other shot a laser at it to get the distance. They used a compass and a clinometer to measure the tunnel’s direction and slope, marked the numbers with a Sharpie onto a waterproof sheet, then copied them onto a piece of colored tape and tied the tape to the reference point. (Back at base camp, Stone would enter the data on his laptop to create 3-D maps of the cave.) This was standard practice in new tunnels and could add hours to a trip. But not here: after three or four hundred feet, the passage abruptly ended. Rather than drop down to rejoin the stream, it had circled back on itself like the oxbow in the sump, ending in a large chamber walled with flowstone. It would take them no farther.

Gala and Short trudged back the way they’d come, their spirits deflated. A dry fossil gallery is the caver’s version of a superhighway: the fastest, safest way underground. But at least they had another option. “There was still the waterfall,” Gala told me, “and it had to go further down.” He and Short strapped on their climbing harnesses and unpacked their rigging. The hammer drill had gone dead after the battery got wet—the fuel cells had all met the same fate—so Gala had to knot the rope around a rock to anchor it. But it held firm as they rappelled down the chasm. Forty feet below, the water thundered into a shallow pool, then slipped down a stair-step streambed to another, much larger pool below. They’d left their dry suits at the top of the falls to air out, so they had no choice but to swim across in their thermal underwear. The water here was a few degrees warmer than higher up in the cave, but still close to forty degrees below body temperature, and the sopping cloth kept it close to their skin. Yet they kept moving forward. “Expedition fever had bitten us,” Short says.

When they reached the far shore, the water cascaded down to yet another pool, twenty feet below. They rigged ropes for the descent, scrabbled down, and swam across, their limbs trembling as the cold sank into them. In the distance, the dusty beam of Gala’s headlamp picked out a pile of boulders in their path, but this only quickened his pulse. It reminded him so clearly of a passage higher up, where a series of pools led to a breakdown pile along a fault line, and then a wide-open tunnel beyond it. “I had this feeling that we were almost done,” he told me. “We will climb these boulders. We will find a huge borehole, and that will open the way to Chevé.”

It was not to be. When Gala and Short arrived at the breakdown pile, it was just the back end of a small sealed chamber—another cul-de-sac. Its boulders were bound together with flowstone, the holes between them no larger than your hand. “There was no air, no anything,” Gala recalls. As for the river, it had found a long crack in the floor less than an inch wide, and spooled through it like an endless bolt of turquoise cloth.

They stood there for a moment in shock, not quite believing that they’d reached the end. They knew that the cave kept on going below, gathering the waters of Chevé beneath them. Yet there was no way forward. Like the cavers in Krubera before the side tunnel was discovered, they had yet to unlock the system’s secret door. Gala looked over at Short—he was shaking uncontrollably now, his wiry limbs lacking all insulation—and was grateful, once again, to have him at his side. “It’s like a friendship during war,” he told me. “So strong an experience, it ties souls together.” He clasped Short’s shoulder and told him to go make some hot drinks while he finished surveying. Then they packed up their gear and began the long climb back to the surface.

Deep caving has no end. Every depth record is provisional, every barrier a false conclusion. Every cave system is a jigsaw puzzle, groped at blindly in the dark. A mountain climber can at least pretend to some mastery over the planet. But cavers know better. When they’re done, no windy overlook awaits them, no sea of salmon-tinted clouds. Just a blank wall or an impassable sump and the knowledge that there are tunnels upon tunnels beyond it. The earth goes on without them. “People often misunderstand,” Short told me. “All you find is cave. There is nothing else down there.”

When I spoke to Stone recently, he was already planning his next trip to Chevé. His team had brought back some intriguing data, he said. Gala’s survey showed that the end of J2 lies directly below a cave entrance discovered in the early nineties. The tunnel beyond it is fairly cramped, but there’s enough air blowing through to suggest that it leads to a larger passage—one that could bypass the blockage in J2. If Stone’s team can connect the two tunnels, then drop down into the main Chevé passage, they might still stitch the whole system together. “Where did the water go a million years ago? That’s what you have to ask yourself,” Stone said. “As a cave diver, you have to think four-dimensionally.” In the meantime, this spring, he was joining an expedition across the river to Huautla, where Jason Mallinson had managed to reach a depth of more than five thousand feet—a new record for the Western Hemisphere. Huautla can never go as deep as Krubera, Stone said, much less the full Chevé system. But it could well be the longest deep cave in the world. Why not see how far it goes?

Base camp in a cloud forest near the Chevé system. Just to set up the camp, Stone’s team had to move six truckloads of material more than twelve hundred miles and up a mountain.

Photograph by Emiliano Granado

That was as good a reason as any. For most of the team, though, it wasn’t the chance at a record that would bring them back, or even the lure of virgin cave. It was the camaraderie underground—the deep fellowship of shared misery. The camps down there were just a few damp tents on rubble, clustered around a propane flame. The food was the same dehydrated stuff they ate up top. A trip to the latrine could be a life-threatening experience—a squat on slippery rocks above a thundering chasm. But after weeks underground, even that smell could lift your spirits. It held the promise of dry clothes and hot coffee, black humor and noisy sex, drowned out by sing-alongs. Gala and Short spent one very good night hollering “C Is for Cookie” until they were hoarse.

On their twenty-first day underground, when they finally emerged from the cave’s rocky clutch, they blinked up at the sun like newborns. Their skin was ashen, their eyes owl-wide and dilated. “I had these mixed emotions,” Gala told me. “I understood that this is the end of J2—nine years of my life, of the most beautiful exploration of my life. It was a sad story.” Yet it had also been the longest and hardest trip he’d ever taken, and it made the return to the surface all the sweeter. The green of the forest, so luminous and deep, seemed nearly psychedelic after weeks of dun-colored earth and the pale wash of his headlamp. The smell of leaves and rain and the workings of sunlight were almost overwhelming.

“It is beautiful here, isn’t it?” Gala had told me when we first met, on a gray, drizzly morning at base camp. “Listen to these strange birds! When I’m back on the surface, just by contrast, I enjoy every piece of my life. Everything is fantastic.” He laughed. “Some people say that all this caving is just for a better taste of tea.” ♦