Great Blue Hole and the deep circle in Lighthouse Reef

Off the coast of Belize, Great Blue Hole breaks the pattern of Lighthouse Reef with a single deep circle of dark water set inside a pale coral lagoon. Lying within the Belize Barrier Reef Reserve System in the Caribbean Sea, it combines extreme depth with the clear outline of an earlier cave system now flooded beneath the waves.

A circular sinkhole in the middle of the reef

Great Blue Hole is a large marine sinkhole near the centre of Lighthouse Reef Atoll, an offshore coral ring east of mainland Belize. The feature is broadly circular and widely documented at over 300 m (around 1,000 ft) across, giving it a footprint that dominates the central lagoon of the atoll.Great Blue Hole is a large marine sinkhole Depth measurements from survey teams and dive expeditions converge on values a little above 120 m (about 400 ft), placing the base far below the typical diving range of the surrounding reefs.over 300 metres across and 125 metres deep

The sinkhole formed in limestone, with geologists identifying it as a karst structure created in several stages during periods of lower sea level when the area stood above the sea.a nearly perfectly round sinkhole in limestone Stalactites and other cave formations discovered deep within its walls point to an earlier system of caverns that later collapsed and flooded as sea levels rose, leaving a single, steep-sided shaft that now opens into the Caribbean.

Part of Belize’s barrier reef and a protected monument

Great Blue Hole sits inside Lighthouse Reef, one of the offshore atolls that form part of the wider Belize Barrier Reef Reserve System along the coast of Belize.located within Lighthouse Reef Atoll This reef complex is recognised on UNESCO’s World Heritage List as one of the largest and most intact coral reef systems in the western Caribbean, with shallow coral gardens, patch reefs and atoll structures framing the deeper sinkhole.part of the Barrier Reef Reserve System, a World Heritage Site

Within Lighthouse Reef, Great Blue Hole forms part of the Blue Hole Natural Monument, a designated protected area that covers the sinkhole and its immediate surroundings.Blue Hole Natural Monument within Lighthouse Reef Atoll The monument lies roughly 70 km (about 43 mi) from Belize City, set in open Caribbean waters where the atoll forms a ring of coral enclosing a shallow lagoon. Seen from above, the contrast between the pale turquoise shallows and the dark centre of the sinkhole makes its outline easy to pick out from aircraft and aerial photographs.

Diving, geology and the view from above

Great Blue Hole is closely associated with scuba diving, with experienced divers travelling to Lighthouse Reef to descend along its near-vertical limestone walls. The steep drop from the reef rim into deep blue water, coupled with overhanging ledges and cave formations at depth, gives the site an underwater landscape distinct from the surrounding coral gardens.a deep circular sinkhole with sheer walls and stalactite formations

The place also has a strong presence in aerial imagery, with photographs capturing the nearly circular outline of the sinkhole set inside the wider atoll.over 300 metres across and about 125 metres deep From the air, the dark blue centre hints at the depth of the shaft, while the surrounding reef crest, sandbars and small cayes show the broader structure of Lighthouse Reef. Together they frame the sinkhole within an arc of coral and shallow water that forms one part of the Belizean section of the Mesoamerican Reef.

Visiting Great Blue Hole: what travellers from Western Europe should know

• Great Blue Hole lies near the centre of Lighthouse Reef Atoll in the Caribbean Sea, roughly east of Belize City off the coast of Belize. Access is by organised boat or aircraft journeys from coastal departure points on the mainland and nearby cayes.
• The site sits in open water inside an offshore atoll, so visits involve time on boats and transfers across reef areas where conditions are shaped by sea state and exposure.
• The official language is English and the currency is the Belize dollar.
• Entry requirements depend on your nationality; UK travellers can check the FCDO travel advice at gov.uk/foreign-travel-advice, Irish travellers the Department of Foreign Affairs at ireland.ie.

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Frequently asked questions about Great Blue Hole

Where is Great Blue Hole located?

Great Blue Hole lies near the centre of Lighthouse Reef Atoll off the coast of Belize, in the Caribbean Sea east of Belize City.

What can visitors expect when they reach Great Blue Hole?

Visitors encounter a large circular marine sinkhole surrounded by shallow coral reef and sandy shoals, reached by boat or aircraft across open water from the Belize coast.

What makes Great Blue Hole distinctive among reef landscapes?

Its combination of extreme depth, nearly circular outline and visible cave formations within a UNESCO-listed barrier reef sets it apart from the surrounding shallow lagoon.