Great Blue Hole

The Great Blue Hole is a dive into geology rather than fish life. From the surface it is the famous navy-blue iris in Lighthouse Reef's turquoise; underwater it is a fast, quiet elevator ride down a sheer wall to a ledge near 40 m where stalactites the size of tree trunks hang from an overhang, dripstone formed when this cavern stood above a lower Ice Age sea. Divers weave between the columns for a handful of minutes, often watched by circling Caribbean reef sharks, then begin the long staged ascent. Jacques Cousteau's 1971 expedition made it legend; discipline keeps it safe.

The moment you come for: Swimming through 40 m stalactites, reef sharks in the bowl, one of diving's most famous single sites.

Topography: A near-circular collapsed cavern about 300 m across and roughly 124 m deep; a shoulder of ancient stalactites overhangs the wall near 40 m.

Current: The bowl is still; the reef rim can carry light surge.

Entry: Day boats cross from San Pedro or Caye Caulker (2–3 hours) or liveaboards moor at Lighthouse Reef; entry over the rim into the bowl.

Hazards: Depth is the whole hazard: narcosis at the stalactite ledge, minutes of no-deco time, and a featureless blue ascent. Follow the guide's profile exactly.

Permits & rules: Park entrance fee; most operators require proof of experience or a prior local dive.

Conservation: A Natural Monument within the UNESCO World Heritage reef system, managed with the Belize Audubon Society; fees fund protection.