Blue Hole of the Red Sea, Egypt
A blue hole occurs when caves are flooded underwater and expand vertically downward, leading to chasms in the oceans. The Blue Hole of the Red Sea is neither the largest nor the deepest, but it is the deadliest, with a reported 130-200 divers perishing in its depths over the last fifteen years.
Experts are not sure why this Blue Hole is particularly deadly, but most explanations center around the existence of ‘the Arch’, a tunnel connecting the blue hole to open water.
In 2000, Russian-Israeli diver Yuri Lipski perished in the Blue Hole while filming himself, with footage of his death later making it to YouTube.