The author swims through a fresh-water cenote in Riviera Maya.

Warm-Weather Escape: Riviera Maya

I float atop teardrop-colored water and can’t stop thinking about the dead. Not the blind albino salamanders or bat corpses I might see—though these would be eerie enough if I encountered a bloated floater amid all this darkness.

Instead, I’m thinking about, you know, the dead dead—the apparitions that freaked the Mayans because they considered these ancient caves a portal to the underworld and reverently tossed golden idols into the maw. If these sinkhole springs, or cenotes, were good enough to scare the daylights out of the Mayans, they’re good enough to sprout a few goose bumps underneath my wetsuit, too. It’s like parading through a flooded graveyard blindfolded.

Still, I have Moises as my geologic and deep-adventure guide through this subterranean pinball machine of fresh water, stalagmites, calcium deposits, beige sand and rock formations that resemble tumbling sand castles. He’s also the man who will save my floundering backside if something rotten happens down here. Which means that Moises, who works as a guide at Río Secreto Reserva Natural (riosecretomexico.com) and looks like a burly Johnny Depp without the affectations and handlers, owns my rapt attention. He says something, and I listen.

If this trip sounds forbidding and both physically and mentally challenging, it can be. And yet it is one of the coolest things I’ve ever done, and even children—I’d probably stick with kids 10 and older—can take the plunge.

The two-hour underworld journey begins above ground with a wild ride from a thatch-hut headquarters 15 minutes from Playa del Carmen deep into a thicket of green scrub flora. Seven of us pile into the back of a dune jeep and travel a mile over pocked and snaking roads that feel like a gag from a failed civil engineer who once worked at the Mexican version of Six Flags.

We clamber out of the vehicle, and Moises greets us warmly before getting down to business. “Does anyone have any back problems?” he asks. We all shake our heads. “OK, is anyone pregnant? No? OK, is anyone claustrophobic or have knee or joint problems?” One young woman tentatively raises her hand; she’s recently had ACL surgery. Moises hands her a cane. “Here, this will help, OK?” We wiggle into our wet suits and super-grip water shoes and crown our sweaty heads with helmets equipped with headlamps.

And off we go, hiking a quarter of a mile through lush palms and cat-sized iguana hideouts to a sinkhole with rickety stairs leading 40 feet below. The clammy-air landing area sits at the mouth of the underground river. Moises tells us that the Yucatán Peninsula has almost no traditional rivers and only a few marshy lakes, which means cenotes are the only potable source of water in the area.

The entire peninsula is like Swiss cheese, and the sunken cave we’re sitting in is active with water—rainwater, actually, which eventually mingles with salt water on its journey to the Caribbean Sea. It infiltrates slowly through the ground, causing the raging stalagmite barrage we’re about to encounter.

Headlamps on, we take tentative steps in the chilly water that laps against our ankles. (The water temperature is 68 degrees Fahrenheit, and it gets slightly warmer the deeper we clop into the cave.) Moises walks through the tunnels like a man who’s been doing this since it opened to the public two years ago. The rest of us alternately train our headlamps on the rich colors and the terra-not-so-firma in front of us—this isn’t a clear, smooth route, since stalagmites and stray rock formations rise from below to trip us, but the passageways remain roughly 20 feet wide throughout the cave.

Water levels vary—up to our knees, down to our ankles, then up to our knees again—as we walk the half-mile route. After 30 minutes, I become submerged to my neck and commit to a slow dogpaddle that carries me through the tunnels at a gentle pace. No one says much as we stop at the cave’s mini-beaches; we simply take it all in as Moises explains the geological rationale for the visual bouquet offered to us by the gods.

We emerge from the hole after two hours, squinting like hungry moles. Río offers all river runners a meal as they head out of the jungle, so we dine, al fresco, on fresh papaya, cantaloupe, red peppers and crab accompanied by crispy corn tortillas. It’s fresh and good and gloriously perfect.

I mention to Moises that I can tell he loves his job. He grins and tells me what I already know: “You are in paradise. The Mayans knew this, and so do I."

For more information about other Riviera Maya adventures, visit rivieramaya.com.