No sooner have we put on our wetsuits than we’re starting to take them off again; summer in Mexico is not the time to be wearing close-fitting neoprene. Luckily, before we’ve completely stripped, the junglemobile arrives, looking more like a large apple crate with an engine attached than a people mover, painted in tiger stripe yellow and black and we hop on the back, wetsuits still dangling by our waists.

The road running through the Yucatàn jungle is far from level and the 10 of us are thrown around like ping-pong balls in a shoebox, ducking as low branches brush our heads. The sun beats down on our pasty white bodies, but covering up would be more of a torture than burning in the sun. Fortunately, it’s only a 10-minute journey before we reach Tak Be Ha – the place of hidden water.

Cenotes – underground pools of fresh water – are found all over Mexico’s Yucatàn Peninsula, some appearing as lakes (the ‘roof’ having fallen in), others only partially open to the elements. More than 1400 cenotes have been identified in the Yucatàn state, but it’s believed that there are well over 4000, and the cenotes and caverns that run beneath our feet make up the longest underground cave system in the world. Hidden Worlds Cenotes is 130km south of Cancun in Xel-Ha and, although seemingly hidden in the Yucatàn jungle, the centre is well served by public transport; just a few miles from the popular beach front resort and Mayan ruins of Tulum.

The IMAX film Journey Into Amazing Caves was filmed here and divers come from all over the world to experience the thrill of cave diving in this incredible environment. It wasn’t the most fun I’d had when I was wet, but it was definitely the most memorable,” reads one comment in the visitors’ book, among others of “incredibly majestic” and “paradise under water”.

With my mask and snorkel in hand, I, too, am hopeful. The temperature immediately drops as I walk down the small ladder into the cavern below. I can hear the sound of water dripping and feel damp in the air; it’s a refreshing change from the heat and humidity outside. Our group slowly makes its way into the cave and we gaze around at the formations: stalactites drop down from the roof like twisted limbs and a few coloured lights shine on large formations growing out of – or is it into? – the water. Our guide Sylvio explains that the Mayans used cenotes as a sacred offering place and it’s thought that the dead were brought to the dry caverns for funerary rituals. He says many of the caverns at the Hidden Worlds Dive Centre have yet to be explored.

As we enter the water, the temperature comes as quite a shock; in front of me someone gradually inches up to their waist and lets out little squeals as the water finds its way into their wetsuit. The views above had been impressive but, as I put my mask on and look below, it’s simply magical. Connecting caverns can be seen, some through small gaps in the rock, others through vast openings; stalactites, stalagmites, columns and flowstones form a gentle palette of pale colours. Long flowing columns reach down next to me and below grow wrinkled fingers of stalactites. It is a natural masterpiece of epic proportions. We swim slowly though the cenote and into smaller chambers.

On the bottom of the cavern lie broken pieces of rock and calcium carbonate and what appears to be fine sand, but the water is crystal clear – its slow movement means that little is carried and visibility only fails where light no longer penetrates the caves. As we move through this labyrinth, the roof gradually closes in until it is just inches from my head. Vast columns appear to support the cavern roof, while pencil-thin limbs drop down and rise up, some just a few inches long, others reach down over a metre below me. I hear my snorkel catch on a few stalactites – perhaps the thin ‘dada straws’ Sylvio told us about – and I dare not look up for fear of impaling my head. We slowly move forward, into a cavern almost totally covered in stalactites, thousands hanging down from the ceiling and thousands more stalagmites poking up from the water below; each no bigger than my snorkel, but so tightly packed that it looks like a bed of nails.

While I have visited many caves in Europe and America, nothing can compare to this. The scale of the formations – in both size and number – is incredible, and the water only adds to the feeling of being in an alien world. My snorkel constantly fills with water as I twist my head too much one way, then the other.

I’m still coughing through my snorkel as I realise we are back in the first cenote, and the tour is over. Few of us speak as we wait to climb the ladder back to the surface, as we are in awe of what we have seen. As I climb, I take a last look back at this hidden world before emerging into the hot jungle. The Yucatàn will never look the same again.”