Dean's Blue Hole

Dean's Blue Hole sits in a bay on Long Island's Atlantic shore, its mouth a modest 25 to 35 m across at the surface. The shaft narrows on the way down, then flares out at around 20 m into a cavern at least 100 m wide — a bell-shaped chamber rather than a straight-sided shaft, which is why a diver descending the line drops through open water without ever brushing a wall. The hole reaches 202 m at its true bottom, the third-deepest known blue hole on Earth, behind the barely explored Taam Ja' in Mexico and Dragon Hole in the South China Sea.

That bell shape is exactly what has made the hole the world's foremost freediving venue. William Trubridge has run the invitational Vertical Blue competition here with AIDA International since April 2008, when its first edition drew competitors from nine countries and produced 23 national and 3 world records; Trubridge himself set a no-fins world record of 92 m here in April 2010, and Tunisia's Walid Boudhiaf reached 118 m at Vertical Blue 2025. The sport's worst tragedy happened here too: American freediver Nicholas Mevoli died on 17 November 2013 after attempting a national record during the competition.

Scuba divers come here as well, though as a single advanced dive rather than a multi-tank trip: local operators out of the island's resorts take guests down into the chamber to the recreational limit of about 40 m, well short of the true floor. Sunlight through the entrance breaks into shafts across the walls, tarpon shoal in the shadows at the edge of visibility, and turtles, reef sharks and the occasional dolphin pass through the shallower water near the rim.

Most visitors never put on a tank at all. A short walk from the road puts you on a sheltered, sandy beach, and swimming or snorkelling straight out over the shaft costs nothing and needs no booking. It is also, by a wide margin, the most dangerous water on Long Island: most of the deaths recorded here are freedivers who pushed past their training rather than divers on scuba, since the body grows denser with depth and the swim back up gets harder exactly when a diver is most likely to misjudge it. Underwater overhangs sit just beneath the cliffs at the surface and again around 18 m down, so the standard advice is to always surface with one hand raised overhead.