The Great Blue Hole is a large underwater sinkhole off the coast of Belize.
It lies near the center of Lighthouse Reef, a small atoll 70 km (43 mi) from the mainland and Belize City.
The hole is circular in shape, more than 300 m (984 ft) across and 124 m (407 ft) deep.
It was formed during several episodes of Quaternary glaciation when sea levels were lower - the analysis of stalactites found in Great Blue Hole shows that formation took place 153,000, 66,000, 60,000, and 15,000 years ago. When the oceans begin to rise again, the caves are flooded.The Great Blue Hole is a part of the larger Belize Barrier Reef Reserve System, a World Heritage Site by the United Nations Educational, Scientific and Cultural Organization (UNESCO) a