From the air
A blue eye.
The TerraMar Project — CC BY 2.0 · Axelspace Corporation — CC BY-SA 4.0 · dronepicr — CC BY 2.0
One of the world's most famous marine sights: a near-perfect dark blue circle in the turquoise Lighthouse Reef, about 318 metres across and 124 metres deep. It began as a limestone cave formed in the Ice Age when the sea was lower; its roof collapsed and the sea flooded it as levels rose. The French explorer Jacques Cousteau made it famous in the 1970s, and it became a bucket-list dive, with divers descending its wall to about 40 metres to see huge stalactites hanging in the gloom, and sometimes sharks. For non-divers the best view is from the air: small-plane flights from Belize City, Caye Caulker or San Pedro circle over the hole, a blue eye in the coral. Long boat trips combine the hole with Half Moon Caye and snorkelling on the reef. The hole is part of the Belize Barrier Reef Reserve System, a UNESCO World Heritage Site since 1996. The boat ride is about two hours each way across open water that can be rough. Use licensed operators; sea trips are cancelled in rough weather, and the hurricane season runs from June to November. Do not touch or stand on coral, do not feed or touch marine life, and use reef-safe sunscreen.
A blue eye.
Underwater stalactites.
Snorkelling.
Lighthouse Reef, about 70 km offshore
The best view is from a small plane, and boat trips add Half Moon Caye and snorkelling, so it makes a good day even without diving.