In the winter of 2012, after 7 months on the sailing ship ATI, an unusual group of friends came to the shores of the Yucatan Peninsula of Mexico. The Yucatan Peninsula is home to the largest and longest flooded caves in the world, tourists regularly visit to enjoy the water holes scattered around the area, but few of them realise that only a few meters underground lies an immense maze of submerged passageways of unimaginable beauty, hundreds of kilometres long. In this film we follow the ATI Cave Exploration Team and features extreme ‘no-mount’ exploration cave diving.