Dean's Blue Hole is one of the most famous diving sites in the world. It is located on the Out Islands of Bahamas, just north of Clarence Town, the biggest settlement of Long Island.
It is the world's deepest blue hole and it is found next to a beach. It is only 25-30 meters in circumference at the surface but once you dive 20 meters deep, its circumference widens to approximately 100 meters.
