The Great Blue Hole

The Great Blue Hole is a nearly circular marine sinkhole near the center of Lighthouse Reef Atoll, approximately 80 kilometers from mainland Belize. Measuring about 305 meters across and 123 meters deep, it began as a limestone cave during periods of lower sea level, when stalactites and stalagmites formed in air. Rising seas later flooded the cavern, creating the deep-blue opening now surrounded by shallow coral reef. Divers descend along steep walls to overhangs and large submerged formations, making this primarily a geological dive rather than a conventional reef dive. The site forms part of the Belize Barrier Reef Reserve System, inscribed as a UNESCO World Heritage Site in 1996.

Fun Fact: The submerged stalactites prove that the Great Blue Hole was once a dry cave, because these formations develop through mineral-rich water dripping in air rather than beneath the sea.