Blue holes are some of the most mysterious and under-explored wonders of the Earth. They serve as the entryway to the world's most spectacular cave systems, attracting free diverswho dare to plumb the mysteries of these underwater chambers.

At more than 600 feet deep, Dean's Blue Hole in Long Island, the Bahamas, is said to be the world's deepest blue hole.It is almost twice as deep as any other explored cave in the Bahamas, according to the Bahamas Journal of Science.

Experts who have dived the site report that it is enclosed on three sides by a natural rock amphitheater and on the fourth side by a turquoise lagoon and powder white beach, according to Bahamas GeoTourism. There is never any swell or waves inside the hole, and visibility is usually between 50-100 feet (15 - 30m).

The bottom of Dean's Blue Hole is rather even, according to WonderMondo, and there are numerous unexplored side passages. Exploration of these passages can be very difficult, however, due to the great depth.

Dean's Blue Hole,named after the family name of local landowners, is also the location of the annual International Free Diving competition, and was the site for the FreedivingWorld Record in 2007. In April 2007,William Trubridge set a world record in unassisted free diving at Dean's Blue Hole, with a dive time of 3’09” and without the assistance of fins, ropes or weight belts, Trubridge reached an unassisted free dive depth of 82 meters (around 269 feet) at Dean’s Blue, according to World Record Academy.

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Over the years, Dean's Blue Hole has become the hub for world-class free diving. Trubridgealso established his free diving school "Vertical Blue" here in 2007.

And while tourists and daring free divers flock to this blue hole, many locals prefer to stay away from this deep-sea wonder. During a shoot for CBS' "60 Minutes," reporter Bob Simon talked to locals, who told him that Dean's Blue Hole was "dug by the devil."

"People have lived on that island for more generations they can count, and we interviewed some old people there who said they had never been to the blue hole, neither had their parents or their grandparents because they were scared," Simon told 60 Minutes Overtime. "They know it would lead to death — and not a happy death — because it's diabolical. If they were to approach it, even floating above the water, it would pull them down, as the devil will do."

The locals' belief may have been strengthened by recent tragedies at Dean's Blue Hole. In November 2013, New York diver Nicholas Melvoli died after an attempt to set a world freediving record at Dean's Blue Hole, CNN reported. Melvoli hashoped to reach 236 feet (72 meters) with one breath of oxygen and without the assistance of fins.When he surfaced, he flashed the OK sign and then lost consciousness 30 seconds later, organizers said.

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