A drowned cave. This is a limestone cavern that formed on dry land during the ice ages, when the sea was far lower, and stalactites recovered from inside date its four growth periods to roughly 153,000, 66,000, 60,000 and 15,000 years ago. Then the sea came up and filled it. What is left is an almost perfect circle 318 metres across and 124 metres deep, seventy kilometres off the Belize coast at Lighthouse Reef, part of a UNESCO World Heritage reef system. Cousteau brought the Calypso here in 1971 and confirmed how it formed. The rim is alive with grouper, angelfish and reef sharks; a 2018 submarine run found a hydrogen sulfide layer around 91 metres, and below that the water is dark, anoxic and dead. PUBLIC, by boat and dive charter.
Mexico
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