Away from the cavern zone, underwater caves exist in perpetual darkness, lit up for mere seconds as cave divers pass through.
A slab of rock that was once part of the ceiling lies like a giant altar on the road through Mexican cave system Sac Actun.
The world explored by cave divers
In the subterranean passages of Mexico's Yucatan Peninsula is an underwater world enjoyed by cave divers.
Eden - the River Run
Cooler fresh water sits on top of warmer salt water, that intrudes into Mexico's caves from the sea. The halocline is what we call this meeting between the two bodies of water.