On a cloudless spring day in southern Mexico, I follow four cavers over a hill studded with pine trees, down 49 dirt steps, and across a grassy field. We approach a towering rock face on the side of a mountain so enormous that it’s difficult to take in all at once. But what drew me here, along with 69 world-class cavers from nine countries, lies at its base.
Beyond a gash that cuts low across the rock face is Sistema Cheve—a cave with the potential to be the deepest on Earth.
As the geologic cathedral comes into full view, I hear a quiet expletive escape Corey Hackley, the caver just ahead of me. This is his fifth year exploring Cheve, and its grandeur still fills him with awe. “The scale of this place is unimaginable,” says Hackley, who’s been exploring caves since he was about 10. “It doesn’t belong on Earth, in my mind.”
Hackley has grown restless in the past few days, forced to linger in base camp for a precautionary COVID-19 quarantine. He calls the hubbub at the surface “suffocating”—a term some might apply to the confines of a cave. But for Hackley and the other cavers, the depths are anything but.
They’re the last frontier of exploration.
In 1990, explorers dumped green dye in the stream flowing into Cheve’s mouth. They discovered the colored water burbling out near the mountain’s base, some 1.6 miles down from the cave’s highest known entrance at the time. If a human could navigate the full length the water did, Cheve would be declared the deepest cave in the world, beating the current record holder—Veryovkina in Abkhazia, Georgia—by almost a quarter mile.
The tantalizing possibility has drawn explorers for decades, and this 2021 expedition was the biggest push yet. Under the leadership of National Geographic Explorer Bill Stone, the cast of cavers clocked more than 1,500 cumulative nights underground and discovered over 12 miles of unexplored passages.
I first meet Stone after he’s surfaced from more than two weeks underground, one of his many trips into Cheve since 1988. Imposing in height and demeanor, Stone asks if I’ve visited the cave yet. I tell him about tagging along with a member of his team.
I had shadowed Reilly Blackwell, who moves through Cheve with the sure-footedness of a dancer performing familiar steps. A mere 10 minutes into the cave, we’d arrived at Cheve’s first series of precipitous drops, clipped into a section of the miles of rope the cavers had rigged, and down we’d gone. Blackwell’s cheery calls had echoed out from the darkness as we’d scurried over fallen rocks and along scalloped walls until arriving at the base of Angel Falls, about a thousand feet deep. Just beyond lay the first of five camps the team had established at that time.
As I gush about that day’s experiences to Stone, a sly look crosses his face. “That’s just the tip of the iceberg,” he says. “Camp One is kindergarten.”
The cavers follow a multilevel labyrinth through the mountain’s underbelly. Carved by rivers over millions of years, some passages are big enough to fit a Boeing 747 plane; others are so tight the cavers can pass only while exhaling to compress their rib cages.
As Stone’s crew tests the limits of exploration, pushing toward record depths and gathering mapping data on the way, camaraderie and teamwork are essential. By the end of the 2021 season, the farthest and deepest camp lay 7.3 miles, or about a five-day trip, from the closest entrance. Only a select few work at that point. Others tend the miles of rigging or search for swifter and safer routes. And all must shuttle heavy packs with supplies and energy-dense foods to stock the camps. For every bite taken underground, Stone says, “a whole chain of people have paid for that in sweat.”
People at Cheve give different reasons for their devotion to caving. Many are driven by an “insatiable curiosity,” Blackwell says. She and Hackley both use the word “compulsion” to describe their desire to seek new passages. But the search can be dispiriting.
Hackley and teammate Bev Shade recall a bleak moment in 2017 while hunting for a way through one cave section. It was named after a picturesque Mexican beach, but in reality—typical of cavers’ wry humor—it was a cramped cleft where water and mud pelted them from a hole in the ceiling. Hackley remembers Shade, covered in slop, turning to tell him, “Sometimes I wonder why I don’t have a different hobby, like bird-watching.”
Such moments forge indelible bonds between the cavers, evident in the laughter Hackley and Shade share while recounting their tale.
The strong community is a big part of what’s kept Shade involved for some 30 years, ever since she attended her first caving event at 16 in her hometown of Austin, Texas. She finds serenity underground too, “away from the chaos of everyday life.”
For many, caving also represents embracing life to the fullest. On a day trip to explore other entrances to Cheve, a trio of team members found a pit whose echo promised great depth, and eagerly lowered themselves as far as their rope allowed. They returned hours later, vibrating with excitement, and reported that beyond their reach were even more passages to explore. “This is why I do it, right there,” team member Mike Frazier declared.
Setting a record is almost beside the point, many of the cavers tell me. “There’s always going to be another deepest cave in the world,” Shade says. “We’re just all trying to do something together. Something that none of us could do by ourselves.”
This story appears in the June 2022 issue of National Geographic magazine.