The Blue Hole - World's Strange Place

The Blue Hole in the ocean off Belize is a spectacular sight from the air and a treat for divers. It's believed to have been formed after the Ice Age, when ice melted and the sea rose, covering what was once a huge cave system. Divers can explore that now-flooded collection of caverns which brims with barracuda, sharks, coral, angelfish and many other sea critters.


source : http://www.virginmedia.com/travel/destinations/features/strangeplaces_2.php