The Great Blue Hole

The Great Blue Hole is the ocean's most famous circle: a sinkhole in Lighthouse Reef atoll, roughly 300 metres across and over 120 metres deep, formed as a cave system when sea levels were lower and drowned when they rose. Jacques Cousteau put it on the diving map in the 1970s. Divers descend past the rim into darkening blue to meet giant stalactites hanging at around 40 metres - a cathedral moment more about geology than fish - while snorkellers work the vivid rim reef above, and scenic flights deliver the aerial view that made the site an icon. It anchors the UNESCO-listed Belize Barrier Reef system.

Highlights

• The dive to the stalactites - the deep swim beneath the rim overhangs.
• The aerial view - scenic flights circling the perfect circle.
• The rim reef - shallow coral and fish for snorkellers.
• Half Moon Caye - the booby colony island usually paired on day trips.

When to go

The dry season from March to June brings the calmest crossings; the trip out is long and open-ocean. Hurricane season peaks August to October. Flights go when weather allows and are best in morning light.

Things to know

The dive is deep, dark and short - advanced certification is required by most operators, and divers expecting reef colour at depth will find grey walls and stalactites instead; many rate the neighbouring Half Moon and Long Caye walls as better dives. Boat days run twelve hours with serious swell possible. Flights cost real money for about an hour. Choose the format honestly by what you want: geology below, geometry above.

Nearby

Half Moon Caye, Long Caye's aquarium walls and the Turneffe atoll.