Exploring the Secret Caves Beneath Mexico’s Biggest Tourist Destination

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All Photos by Klaus Thymann

The hole in the Earth is shaped like an uppercase B—a ragged shaft plunging into the forest floor beneath us. It can’t be more than two feet wide. Klaus Thymann, a 42-year-old Danish photographer, lays a pair of aluminum air tanks under a sapodilla tree as Luís Leal, a 50-year-old cave-diving instructor with a Trotskyesque beard and a tan mesh hat, shines a flashlight into the hole. The machete-cut path that brought us here is barely visible through the vine-clogged jungle, and all around, the strange whoop of the blue-feathered motmot bird reverberates.

Thymann approaches the opening, a mop of sun-bleached hair tumbling forward as he leans over to have a look. “Ah, wow,” he says.

Leal grins, eyeing the same thing. “Crystal-clear blue water,” he says.

“Luís,” Thymann says. “Let’s get into a wetsuit.”

Leal unzips a giant duffel bag and heaves out a long, white rope ladder, lashes it to a nearby tree, ties it off with a carabiner, and unfurls it into the hole. After squeezing into our Neoprene, we descend awkwardly, trying to avoid a wall of razor-sharp limestone. And then, at about 25 feet deep, we drop into the clearest blue water I’ve ever seen. Thymann and Leal do one last equipment check, turn on their dive lights, and disappear into the abyss. I watch as their lights recede into a crack in the limestone. Far above, the Mexican sunshine filters through the jungle in the tiny B-shaped window. 

As far as we know, we are the first humans to enter this water. 

The other Yucatán is mostly invisible. Carved like a neural network into the porous limestone below are more than 900 miles of underwater caves and caverns. And that’s only what’s been explored so far. Divers have found everything from ashes of prehistoric fires to human skulls, bone flutes, and the eight-foot-tall skeletons of extinct giant sloths preserved among the stalagmites and stalactites. Occasionally the ceilings of these caverns collapse, forming cenotes, or sinkholes. Mayans believed that cenotes were portals to the underworld. They are, verifiably, the region’s only source of drinking water, because the porous limestone makes surface rivers and lakes impossible. Many of these once-hidden oases have been transformed into tourist destinations where van loads of snorkelers and divers soak in the mind-bogglingly blue waters of cenotes like Misterio Maya and Rio Secreto.

The jungles of the Yucatán still hold some secrets, though. New cenotes are being discovered, and scientists believe the distance of surveyed caves represents less than half of what’s actually down there. In a world where virtually everything is Yelped, FourSquared, geo-located, Pinned, and Snapped, the Yucatán’s cenotes are a true last frontier, one of the only places on Earth where you can step foot (or fin) where no one’s been before you. 

But as development explodes along the Riviera Maya, this secret world is facing threats it may not be able to withstand. As a result, for divers like Leal and Thymann, exploring cenotes isn’t a hobby. It’s a race to discover and raise awareness of a natural wonder we’ve only begun to understand—before it’s too late. 

Leal’s Cenote obsession struck him hard and fast 24 years ago. A lawyer in Mexico City at the time, he was vacationing with his family in Akumal when a diving guide took him to a sinkhole. There, Leal drifted fishlike among the stalactites. “In 45 minutes, it completely changed my life,” he says. He gave up law and relocated to the Riviera Maya, where he trained to become a cave-diving instructor.

Leal now runs a small dive shop near the entrance to Dos Ojos, one of the larger cave systems in the area. But teaching is a day job for divers like Leal and Thymann. The real draw is “laying line”—that is, being the first to explore new passages, tie off guidelines so other divers can find their way, and plug the survey data into mapping software back on dry land. Apart from the thrill of getting there first, the glory comes from connecting the dots—linking up lines from new passages to existing ones to form a complete system— and having the privilege to name your find. 

That’s been true since the 1980s, when the first gringo divers began heading to the Yucatán to explore these mysterious caves. Back then, much of the jungle around Tulum was designated as communal farmland, which meant nobody really owned the cenotes. Over the past few decades, however, farmers have been subdividing the land and selling parcels off to the highest bidder. The legal grounds for such sales are murky. Last year, for example, a series of government raids rocked Tulum’s tequilas-and-tablas vibe. Hundreds of men wielding sticks, metal pipes, and machetes stormed 17 properties (including private hotels and homes along the shoreline) and immediately evicted the owners. In the fallout, journalists exposed an elaborate system of fraud to bilk dream seekers out of their savings—along with the property rights they thought they’d purchased. Competing land claims, fake contracts, forged deeds, and corrupt government officials and judges had paved the way for the ugly spectacle. Yet the raids were legal—the armed agents were acting on a judge’s orders. 

These days, finding a cenote on your land can be a mixed blessing. If you’re on the jungle side of Highway 307, where land is less valuable, it can be like striking oil. “A hectare of land in the jungle here could be worth maybe $50,000,” Leal says as we rattle over limestone roads on our way back to his dive shop. “If you find a nice cenote, it could be worth $500,000.” That’s because even though the federal government owns the waters and the caves, landowners can charge admission to divers. Leal and his pals often get calls from locals when they find a hole on their property. Should that hole open into a surreal underwater cavern, that landowner has a source of income for the rest of his life. 

On the other hand, if you’re a big developer on the ocean side of the highway—where it’s illegal to build too close to an underground cave system—the last thing you want to hear is that your land can no longer accommodate those 10-story condos in your master plan. 

Though Mexican law prohibits polluting federal waters, the underground river system itself—along with the fragile arterial walls that define it—lacks blanket legal protection. And with the revenue from 5 million annual tourists at stake, not everyone wants rules that could slow down the seemingly endless flow of fresh cash. 

On a Friday afternoon last spring, Leal pulls his mud-spattered ’90s British Land Rover into the limestone parking lot of Casa Cenote—the turquoise chasm that converted him from lawyer to full-time cave diver. Thymann readies the underwater housing on his DSLR camera, test-firing the flashes in preparation for the dive. The pair have been diving together for years, since Leal gradually trained and certified Thymann to be a self-sufficient cave diver. Thymann, in turn, featured Leal in his documentary about cenotes, Flows, which premiered in London last July. Watching them work together is like watching a Venn diagram of Danish efficiency colliding with laid-back coastal Mexican vibes. But they overlap at a serious shared passion for conservation and exploration.

Looking out over Casa’s swimming-pool-blue surface, shimmering under the emerald green mangroves, it’s easy to see how the place sparked an obsession. Casa’s waters arrive filtered from deep within the jungle, exiting the pool through a tunnel under the two-lane road we drove in on and finally spilling out into the ocean in front of the open-air restaurant across the street. We enter the water in the early afternoon and descend past a group of snorkelers into the caverns. Striped fish flit around undulating grasses in an azure dreamscape. We go deeper, and Leal points out the remains of a sea turtle framed in translucent stalagmites. On the surface, as I unzip my wetsuit and come back to reality, it’s already enough to make me think about cashing out and ditching the city for good. 

“Amazing place, isn’t it?” Leal says. 

It’s also a study in how rapidly this area has changed—and what it risks losing. When Leal first came here, the road in was deserted, with space for one car by the cenote. Now the road is lined with towering beachside McMansions with only a few feet between them. Just in the last two years, Leal claims, the cenote’s owners dumped fill over the protected mangroves (illegal since 2007) to widen the parking lot for the droves of new visitors who pay them a $5 admission. “It’s very bad,” Leal says over lunch at the seaside restaurant across the street, where everyone seems to know him. He’s reflecting on the increased popularity of Casa Cenote. “It’s become a place to train open-water divers, so it’s very crowded.” 

The designation Riviera Maya is a recent one—the brainchild of developers keen on attracting a new wave of affluent sunseekers to an area that, until the 1990s, was identified as Costa Turquesa on official maps. It worked. In the 1970s, Cancún was little more than a fishing village. Now the mega-resort mecca hosts 5 million tourists a year. Forty miles south, Playa del Carmen—once the sleepy antithesis to Cancún’s sombreros-and-lasers vibe—has almost doubled in population in the last decade to become Latin America’s fastest-growing city. Even Tulum’s trademark serenity has faded, as big trucks snarl past boutiques on the Zona Hotelera and the din of new construction drowns out the tabla beats. The growth shows no sign of stopping: The Mexican government expects a tenfold population increase by 2030. 

You don’t have to be a cave diver to see the effect such development has had on the cenotes. In 2015, a 40-foot section of the Cancún–Playa del Carmen highway collapsed as the cave beneath it finally succumbed to the weight of traffic. Playa del Carmen’s sprawl has completely engulfed a pair of cenotes, which are so clogged with garbage that volunteer groups must regularly clear them out. 

After Thymann and Leal finish lunch, we pile into a car and head north past the guarded hotels and walled subdivisions of Highway 307. Thymann points through the window at the massive limestone arches of the Bahia Principe resort, towering over a manicured lawn. “I went in there last year pretending that I wanted to buy a place,” he says. “And the guy proudly told me they’d dug down into the cenotes to make the golf course. He said they even hired a diver to connect them.”

A few miles north of Playa del Carmen is the entrance to the exclusive 1,600-acre resort development of Mayakoba, home of a Rose- wood Hotel, a Fairmont, and 10-time host of the PGA Tour OHL Classic. Touting itself as the “Venice of the Riviera Maya,” Mayakoba features eight miles of blue waterways. Of course, there are no natural aboveground waterways in the Mayan Riviera, so Mayakoba had to make them. “What we did is excavate—which is easy because this limestone is not so hard to break, you know?” the development’s general manager, Agustín Sarasola, told me. “So with not-big machines you can create those canals. In some areas we used little explosives.” He’s been pleased with the results. “These canals unify the whole development, making it possible to go from one amenity to another amenity with a little boat,” Sarasola says. 

Farther up the road, we pull into a massive development called Puerto Aventuras, where 7,000 residents have access to the area’s only marina, a nine-hole golf course, a small constellation of bars and restaurants, a Starbucks, a swim-with-dolphins experience, penned manatees, and captive sea lions. Leal frowns his way past the sea lions and takes us down a palm-lined boulevard, where he says developers broke through a cenote to build a seawall. Sure enough, in the bottom corner of a canal below a deserted condo, turquoise water pours out of an enormous crack into the man-made waterway. 

“Every time there’s a channel cut into the geology, it decimates the ecosystem and changes geochemistry, and it means that you lose all the freshwater,” says Patricia Beddows, assistant chair of Northwestern University’s Department of Earth and Planetary Sciences and one of the world’s foremost experts on cenotes. “It’s a categorical stressor on the ecosystem.” 

Another stressor is what’s flowing into the cenotes. According to Mexico’s Ministry of Environment and Natural Resources, 80 percent of the approximately 6,000 cenotes in the Yucatán Peninsula have pockets of contamination—and sewage is one of the biggest culprits. The porous limestone means that nothing stays aboveground for long. But the Mexican government doesn’t regulate the Yucatán’s fragile aquifers any differently from those in rest of the country. Most of the larger hotels are required to have their own sewage-treatment facility, but they often malfunction. Even treated sewage contains contaminants that can disrupt the cenotes’ fragile ecosystem. 

All that water, of course, eventually empties into the Caribbean, where scientists have measured a shocking 50 percent die-off of the local reefs over the past 25 years. And not everyone in the region’s fast-growing cities, including the hundreds of thousands of workers moving here to service the tourism boom, hooks into the municipal system. 

Gonzalo Merediz Alonso, executive director of local conservation nonprofit Amigos de Sian Ka’an, has been developing stricter environmental certifications for hotels and other developments in the area, but they’re still voluntary. He’s also helped the city of Tulum offer incentives for citizens to hook up to the municipal sewage system. But keeping up with the growth has proved challenging. “The problem is the population grows faster than the government’s capacity to provide services like sewage treatment,” Merediz Alonso says. “So you build new houses, but they don’t connect.” 

“So where does all the waste go?” I ask.

“In the best cases? A septic tank,” he says.

And in the worst cases?

“Right into the aquifer.”

Last year, the Mexican government designated 5.7 million hectares of reef off the coast of Quintana Roo as a new biosphere preserve, making it the largest protected area in the country. But the cenotes that drain into the Caribbean—directly affecting the health of the coral—remain unprotected. This, Thymann says, is what motivates him to push further. Every picture, every foot of new guideline, is one foot closer to protecting a natural wonder that both he and Leal imbue with humanistic qualities. Leal calls the cenotes “the veins of the Earth.” Thymann is more matter-of-fact. “It’s really straightforward,” he says. “We have a pristine environment, clean water, archaeological sites. We should just preserve it.” 

“If they shoot me in these, I die standing up!” Alessandro “Alex” Reato—a 48-year-old cave diver with wide eyes, a thick Italian accent, and a contagious laugh—is cracking a joke about the stiff leather of his Italian army boots. It’s Sunday morning, and we’re back in the jungle, this time farther south, in search of another remote cenote. Reato slashes at a tunnel of vines with a machete, clutching an orange GPS device in his other hand. Behind him, Thymann follows with his camera and a bag of gear as two local workers, Enrique and Federico, bring up the rear with more tanks and equipment.

A couple of months ago, Reato caught word of a new cenote from a local landowner who’d just discovered it on his property. So far, Reato and Leal (who isn’t accompanying us today) are the only people who’ve dived it. But Reato has surveyed enough to know that it connects to the 58-mile K’oox Baal system nearby. Over the years, Reato has become an accomplished cartographer, surveying complete cave systems, then illustrating and subsequently publishing the maps. With 5,800 logged dives and 38 miles of virgin passage to his name, he is quick to differentiate his obsession from “recreational” diving. 

“If I don’t come back with a map, I’m a loser,” he says. “It’s just kids playing in a pool.” 

Soon we arrive at a jagged, four-foot oval crevice where two lashed-together ladders descend to the water 20 feet below. Thymann and Reato suit up and show each other how they’ve set up their equipment—where they’re stowing their multitools, line cutters, backup lights, and supplies. They do this for safety reasons, in case one of them has to get the other out of a jam.

Yellow-beaked Yucatán jays squawk around us as huge iridescent blue butterflies flutter in the dappled sunlight. We climb down. The bottom of the cave smells like mushrooms and guano. A tiny fish darts around the blue water beneath an undulating reflection of the ladders above. 

Reato and Thymann embark on an hour-long journey to survey the caves and come back ecstatic. 

“K’oox Baal is 70 meters longer today,” Reato says. 

“We got some magic today,” Thymann agrees. 

As Thymann climbs the ladder, Reato offers to take me down to have a look around. I let the air out of my buoyancy vest and sink slowly beneath the surface. 

What I see leaves me on the verge of tears. 

The tiny opening gives way to an immense underwater cathedral, maybe 100 feet wide, adorned with all manner of stalactites and stalagmites—curtains and columns of dripping calcite encircling a weird cone of debris that’s settled under the sinkhole’s entrance like a Surrealist altar. We circle the scene as Reato points out the tiny crevice that leads to untold miles of unexplored tunnels. Then Reato motions at me to cover my light and turn toward the opening. It’s high noon, and a single shaft of emerald-tinted sunlight pierces straight through the hole into the crystalline waters below—striking the top of the cone like a laser beam. 

We hover there, suspended in the darkness—two lost disciples facing the crumbling altar. 

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