The Pit is an incredible dive site in Tulum Mexico. A fresh water sinkhole with unlimited visibility a hydrogen sulfide layer (aka the cloud) and an island of debris (with its own tree which you can see in the picture) says photographer Tom St George.
Marble Caves of Patagonia in Chile – Lake Carrera. The lake is on the border of Argentina and Chile, and the caves are located on the side of Chile. The caves are the three main grotto: Chapel (La capillaries), Church (El Catedral) and Cave (Cueva).