The Great Blue Hole is a large marine sinkhole located east of the coast of Belize in the Caribbean Sea. Jacques-Yves Cousteau made the first explorations at this site in 1971 with his ship Calypso to monitor its depth. The cavity is almost perfectly circular, over 300 metres wide and 123 metres deep. As part of the Belize Barrier Reef it is recognized by UNESCO as a World Heritage Site.






