A blue hole or vertical cave is found on many different locations worldwide naming a few: The great barrier reef, Belize, Egypt,... Its shape is more or less a circle and is quite deep, showing a deep blue color and the surroundings are rather shallow. The deepest of them all is located in the Bahamas with a depth of approximately 200 meters. Most of these caves hold fresh water as well as salt water. Yes, this is definitely a must have dive tshirt ! Scuba dive clothing that stands out!