Some of the most decorated underwater caves on earth, Dan's Cave and Ralph's Cave hold stalactite formations, calcite rafts and…Some of the most decorated underwater caves on earth, Dan's Cave and Ralph's Cave hold stalactite formations, calcite rafts and helictites that National Geographic photographed as a landmark expedition. Below a hydrogen sulphide layer, the anoxic water preserves fossils, Cuban crocodile skulls, tortoise bones and human remains thousands of years old. The 2009 National Geographic expedition into Abaco's blue holes recovered fossils that rewrote Caribbean prehistory, including extinct crocodiles and a Lucayan skull. The anoxic layer means nothing decays, the caves are a time capsule of the last 12,000 years. Anchorage: Anchor in the Sea of Abaco or at Sandy Point and travel overland. Hazards: Full cave environment with a hydrogen sulphide layer and delicate decorations. Cave certification, guideline protocol and local guides are non-negotiable. People have died in Bahamian blue holes. More