There are no surface rivers in the Yucatán Peninsula, the population’s freshwater supplies coming from a vast system of underground caves and sinkholes, known as cenotes (dzonot to the Maya). Four thousand cenotes and hundreds of miles of caves are believed to lie within the Yucatán Peninsula, all originating from the wreckage of the celestial impact, 65 million years ago when an object similar to an asteroid plunged through Earth’s atmosphere and struck the seabed of the still-forming Gulf of Mexico.

As the Yucatán Peninsula rose from the sea over tens of millions of years and rainwater and streams ate through the cracks in the fractured limestone, it absorbed carbon dioxide and formed carbonic acid. This acid, in turn, eroded the rock, carving out vast subterranean labyrinths that became underground rivers and caverns which stretched beneath the entire peninsula and throughout Mesoamerica.

During the last ice age, water levels dropped, draining the caves. That allowed extensive stalactites, stalagmites, and other calcium carbonate formations to form within the karst geology. Eventually the ice melted and the sea rose, reflooding subterranean dwellings.

*

The Caves of the Hidden Woman, or Grutas de Xtacumbilxunaan, are located just outside Bolonchen, Mexico. A night after she had arrived in the village, Lilith Robinson, armed with lanterns, rope, a map, and spelunking supplies, followed her imaginary uncle down a rarely tracked path through the Mesoamerican jungle until she came to a rocky mountainside. Hidden among the foliage was an entrance to a cave.

‘What’s inside?’ Lilith asked Don Rafelo.

‘Your destiny.’

With the lantern clenched between her teeth, Lilith got down on all fours and crawled through the opening.

The glow from her light revealed a claustrophobic limestone tunnel, its diameter no larger than a manhole cover. For half an hour the teen continued on her hands and knees, forcing her way into the humid darkness until the tunnel opened to a cavern the size of an elementary-school gymnasium.

The walls of the subterranean room glowed fleshy pink in her light. Dripping sounds echoed eerily in the chilly air. Stalactites and stalagmites leaked calcium-laden water.

She turned as Don Rafelo appeared behind her.

‘Where are we, Uncle?’

‘Xibalba Be, the road to the Underworld. We must descend five levels to reach Lucifer’s chamber, this is only the first.’

Lilith aimed the beam of her flashlight down a winding embankment leading straight into the bowels of the earth. ‘Down there?’

‘It is where he awaits.’

Tying off one end of a nylon rope to a stalagmite, she made her way backward down the slope, the limestone beneath her boots slippery, the cavern walls to her left glowing shades of violet and crimson in the lantern’s light.

She continued descending backward into the bowels of the mountainside, her exit disappearing above her light’s reach in suffocating darkness.

At 108 feet, the steep slope leveled out.