A submarine sinkhole in the Red Sea, 130 metres deep and 60 metres across at the surface, famous for its colour and infamous for the highest concentration of fatal diving accidents of any site on Earth.
The Blue Hole of Dahab is one of the most beautiful natural features in the Red Sea, and it is the most deadly dive site in the world. These two facts are directly connected.
The hole is a vertical shaft in the coral reef, 130 metres deep and 60 metres across at the surface. The water inside is a deep cobalt blue that is visually distinct from the lighter turquoise of the surrounding reef — the depth absorbs the wavelengths that the shallow water reflects, and the result is a column of colour so dark and so deep that staring down into it produces vertigo. The edges of the hole are covered in coral at the upper depths, the fish population dense and varied, the visibility exceptional on calm days.
At 56 metres depth, there is an arch in the wall of the hole — a passage that connects the hole to the open sea. It is 26 metres long. To swim through it from inside the hole to the open sea, a diver must descend to 56 metres and then pass through the arch, ascending into open water. At 56 metres, nitrogen narcosis sets in — a state of impairment that mimics alcohol intoxication, affecting judgment and motor control. At 56 metres, the body''s nitrogen load is building toward toxicity.
The Blue Hole has claimed more than 150 lives, many of them experienced divers who attempted the arch and did not make it through. A plaque above the site lists their names in multiple languages. The hole itself is unchanged by all of them: blue, deep, and still.