Using an electric drill to attach bolts to the rock face, the couple rappelled down to its base. They followed the river until it “closed into a gap you couldn’t even put your hand in – the bottom of the cave,” Short said.

Even if exploration – not science – was the reason we were there, says expedition leader Bill Stone, mapping cave systems like this paves the way for future scientific expeditions.

“Caves need to be protected,” says Hazel Barton, a professor of geological sciences at the University of Alabama. Barton is a geomicrobiologist who studies microbes that live in some of the most extreme environments on the planet – and one of the scientists who followed Stone’s footsteps into the Sierra Juárez mountains.

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For more than 20 years, Barton has studied microscopic life, found deep underground, that can survive extreme starvation. His research deepens our understanding of antimicrobial resistance (AMR), and even what photosynthesis capacity – in what would appear to the human eye as total darkness – could tell us about the possibility of extraplanetary life.

“A kilometer from the entrance, and there’s still photosynthesis,” Barton explains, “but it’s being pushed toward the near infrared wavelength. There is stars that emit only in these wavelengths. So this could help us understand how life is possible on other planets,” she says.

Exploring caves, Barton says, is the closest thing to being an astronaut without going into space. “You are the first person to see something, your first prints are yours. In 10,000 years, the footprints I left in Lechuguilla Cave in New Mexico, or in the Tepui Caves in Venezuela, might still be there.

Walking out of Wookey Hole into the sun, I find my senses heightened – the smell of damp foliage, the echoes of birdsong, the breeze on my skin, the warmth of the sun. I feel like I woke up from a dream. “It’s hard to impress people these days,” Short says, “but you can come here and see something different every time.”

Hundreds of cave entrances are known on Earth, the Mooneven March. Many have never been explored. If we dare to look into the darkness, what might we find hidden beneath the surface?

You can hear Phil Short speaking on the BBC podcast More Wow here.

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