A giant marine sinkhole in Lighthouse Reef
The Great Blue Hole is a vast marine sinkhole around 300 metres across and over 120 metres deep, formed when the sea rose and flooded a cave system at the end of the last ice age. Jacques Cousteau made it famous. Divers descend to see stalactites in the walls and reef sharks cruising below, and scenic flights reveal its striking circular shape from the air. Day trips usually combine the dive with the reef walls of Lighthouse Reef and Half Moon Caye, where red-footed boobies nest.