Banco Chinchorro

Thirty kilometres off the Costa Maya lies the largest coral atoll in the wider Caribbean basin: Banco Chinchorro, a 40-by-18-kilometre ring of reef enclosing a turquoise lagoon, protected as a biosphere reserve and famously fatal to shipping. Centuries of hulls met its windward wall - Spanish galleons through twentieth-century freighters - and their remains, from anchor gardens and cannon to the photogenic rusting bulk of a stranded cargo ship, make the atoll a wreck-diving destination of genuine rank. The living reef outdoes the dead ships: with no rivers, no runoff and almost no people, visibility runs to forty metres over coral cover the mainland lost decades ago - forests of elkhorn, walls of barrel sponges, clouds of grunts, reef sharks on patrol and lagoon flats where American crocodiles cruise the mangrove keys, dived with specialist operators in famously clear encounters. A handful of fishermen's stilt huts on Cayo Centro - palafitos standing over the shallows - shelter the cooperative lobstermen and the rare overnight trips. Crossings are open-sea and weather-called; the reward is the Caribbean as it was.

What you actually see

• The wrecks - centuries of ships on the windward wall.
• The untouched reef - elkhorn stands and forty-metre visibility.
• The stilt huts - lobster cooperative palafitos on the keys.
• The crocodile flats - specialist encounters in the lagoon.

When to go

April to August for the calmest seas and reliable crossings; winter northers cancel freely. Book with the few licensed Mahahual and Xcalak operators days ahead.

Honest expectations

The crossing is long, open and sometimes rough - this is an expedition day, not a beach trip. Costs reflect fuel and permits. Day trips see a fraction of the atoll; divers get the headline sites.

Nearby

Mahahual's malecon and Xcalak's village are the gateways; Bacalar's lagoon rounds out the far-south circuit ashore.