World's deepest blue hole (Bahamas Tourist Office)

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Blue holes are collapsed underwater caves and a diver's heaven to boot. From above, they resemble dark circular holes against the lighter blue sea. Dean's Blue Hole on Long Island in the Bahamas is the world's deepest known at 202 metres deep and 76 metres wide, adorned with stalagmites and stalactites. Packed with crustaceans, it's also popular with nurse sharks.

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