The Great Blue Hole

The Great Blue Hole is a submarine sinkhole off the coast of Belize. It’s one of the top scuba diving sites in the world and the water is 407 feet deep. It lies near the center of Lighthouse Reef, a small atoll 70 km from the mainland and Belize City. The hole is circular in shape, over 300 m (984 ft) across and 124 m (407 ft) deep. The Great Blue Hole is part of the larger Belize Barrier Reef Reserve System, a World Heritage Site of the United Nations Educational, Scientific and Cultural Organization (UNESCO).
           The Blue Hole of Belize is unique and is the only Blue Hole that can actually be seen from space with the naked eye. It was originally an above ground  cave and as the water levels rose the weight of the water caused the roof to collapse and form an almost perfect circular hole.
          Although the Great Blue Hole is most definitely great, it is not the deepest. That title is held by Dean's Blue Hole, located in the Bahamas, with a depth of 663 feet.