Blue Holes are an amazing natural phenomenon occurring around the world in coastal regions. They’re usually underwater caves or sinkholes, and though they can be on land, the ones that formed in the water are obviously more spectacular.
The name comes from the dramatic colour contrast between shallow waters around them and the depth inside the holes. Most of the blue holes were formed during ice ages, when the water was level was lower than today, and they were initially caves. After the sea level rose, the caves sinked and formed the deep holes.
Blue holes are great diving spots which you can enjoy in many places around the world, though the most famous ones are in Bahamas, Belize, Australia and Egypt. Explore some of the greatest blue holes in the gallery below!
Edit: Recent studies showed that the blue hole in Belize held a clue to demise of Maya civilisation. Drillings in the hole’s floor showed that the period between 800 and 1000 A.D. was a time of unusual drought, which affected the whole civilisation and might have caused its collapse. More info here!