Blue Hole, Dahab

A submarine sinkhole in the reef just north of Dahab: a near-circular shaft about 130 metres deep, dropping straight down from a shallow rim only a few metres from the shore. From the beach it appears as a disc of deep navy in the middle of turquoise water.

For snorkellers

The rim is genuinely excellent and completely safe. Hard coral in the shallows, walls of fish, and the eerie experience of swimming from bright shallow water out over a lip beyond which the bottom simply vanishes into blue. Most people come for exactly this and never go deeper.

Entry is easy from the shore, the water is calm, and there is a line of small cafés on the rocks where you can sit afterwards.

A serious warning

The Blue Hole has a deserved reputation as one of the most dangerous dive sites in the world. The danger is not the hole itself but "the Arch" — a tunnel at around 52 metres connecting the shaft to open sea. At that depth nitrogen narcosis impairs judgement badly, the tunnel is longer than it looks, and divers who misjudge it have run out of gas inside.

Memorial plaques on the cliff above record many deaths. Snorkelling and shallow diving here are safe and lovely; the Arch is technical diving that requires appropriate training, gas and support. Do not let anyone talk you into it otherwise.

The hole is a karst feature: a limestone cave system that formed during the last ice age when sea levels were far lower and this was dry land. Rainwater dissolved the rock from within, the roof of the chamber eventually collapsed, and when the sea rose again the shaft flooded — the same process that creates cenotes in Mexico and blue holes in the Caribbean.

The Arch is a former cave passage that once ran out to the open hillside and is now a submerged tunnel through the reef wall.

A freediving arena

The site's shape — deep water immediately accessible from shore, with no current and no boat needed — makes it close to ideal for freediving, and it has become one of the world's principal training and competition venues. Several world records have been set here, and on any given morning there will be athletes on the rim working on breath holds.

Dahab itself

Dahab was a Bedouin fishing village that became a backpacker stop in the 1980s and has kept more of that character than the resort towns further south. The seafront is still low-rise, the restaurants are still cushions on the ground, and the town's economy runs almost entirely on diving.

The Bedouin community here, principally the Muzeina, remains closely involved in the businesses along the shore — the camps, the camel routes into the interior and the Blue Hole cafés are largely theirs.