A WATERY UNDERWORLD

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Under the sweltering surface of the Yucatán peninsula are caverns full of cool fresh water. Tom Wainwright takes the plunge to get to the bottom of their role in Mexican history ...

From INTELLIGENT LIFE magazine, November/December 2011

A hundred feet off the Caribbean coast of Mexico, where the water is as clear as tequila, the fish know that something is up. A great silvery shoal is wafting back and forth against an invisible barrier, reluctant to go any farther. If you look closer, just beneath a rocky overhang, you see that something about the water is different: here it swirls and shifts, from the warm, salty blur of brine to sudden, chilly, clear windows. And if you dive a few feet down you see what lies beneath the rock where the fish don’t dare to go: the narrow mouth of a long, dark cave leading beneath the sea bed and back towards the land, gently pumping out icy fresh water.

Mexico’s Yucatán peninsula, which millions of years ago formed part of the sea bed, is like a giant stone sponge, riddled with underground caverns which are flooded with clear, filtered rain water. The cave systems, which are said to include the world’s largest single network, leak out into the open sea, leaving Mexico’s Caribbean coast dotted with hidden entrances to the underworld. When the waves are calm, a visitor with a slender build and a pair of oxygen cylinders can duck down into the dark passages, to emerge a nervous few hundred yards inland, along with freshwater fish and a few bewildered crabs that have somehow clawed their way through the darkness.

The fresh water provides a blessed relief from the baking crust of Mexico’s deep south, where temperatures hover around 30 degrees Celsius and the oppressive humidity leaves your clothes permanently damp. Dotted around the peninsula like cigarette burns in the rock are more than 2,000 natural sinkholes known as cenotes—from the Mayan word dzonot, meaning abyss—which lead down into the underwater reservoirs. For hundreds of years the cenotes have given the locals access to fresh water in a landscape that lacks any rivers or lakes. Fishermen have even been able to stock up on drinking water far out at sea, where a handful of underwater cenotes called ojos de agua (eyes of water) gush fresh water into the Caribbean in a few secret spots known to the trawlers.

These days, the cenotes are used more for fun than survival. A little way into the jungle beyond the coastal road to Tulum lies Cenote Calavera, or the Cenote of the Skull. A barrel-shaped attendant is doing his best to persuade tourists to ignore the sinister name. “Come and swim, there’s no one else here today. You don’t even need your clothes!” For a few pesos you are led through the trees to a patch of white rock, where three narrow shafts bore into the ground. If you scramble up onto a higher spot of land, you can see that the holes in the rock form two eyes and a grinning mouth, in the shape of a toothless skull. Deep within the eyes, clear water sparkles. That’s how the cenote got its name, then? “Also the human sacrifices,” our cheery guide explains.

A dark leap into a skull-shaped burial pit may not sound all that appealing. But when the sun is like a blowtorch on your neck, the chilliness of the underworld seems a tempting prospect. I edge forward to the lip of the skull’s mouth, take a breath and step forward into thin air, tumbling into the darkness of the skull’s throat. The water, which I send shooting up out of the skull’s mouth like spit, is icy. When I come up for air, I can make out the walls of the cavern, lit by three shafts of light streaming in through the eyes and mouth in the roof of the cave. Fish nibble my toes. A few seconds later I nearly jump out of my skin as what sounds like booming laughter echoes around the cave. As I scramble for the rope I realise it’s just the noise of the waves from my jump slapping the sides of the cave, where they create an echo that rumbles through the cavern. Ducking down under the water, I can see where the cave’s edges slope away into pitch-black tunnels, leading off to other cenotes deeper in the jungle. The water suddenly seems chillier as I think about what those fish would have nibbled on here a few hundred years ago.