SHIMMERING REEFS, MIGHTY RUINS

Cozumel is the busiest cruise port in the Caribbean, and it is busy for a straightforward reason: the reef starts a few hundred yards offshore, the water is eighty-five degrees, and the visibility is routinely over a hundred feet.

Which pier you get matters. Punta Langosta is in San Miguel and you can walk into town. Puerta Maya and the International Pier are three to four miles south: a fixed-rate taxi, not a walk. The ship’s daily paper says which one you are on; check it before planning a morning in town.

The diving is genuinely world class and the snorkeling is nearly as good. Palancar is a drift dive, which means the boat drops you up-current and picks you up downstream; you do very little work. If you would rather not get on a boat, Money Bar and Dzul-Ha are reef-off-the-beach and cost a taxi fare.

The mainland is possible but tight. Tulum is a ferry plus a drive plus the same again coming back. On a ten-hour call with a ship’s excursion it works; on a seven-hour call independently it is a bad bet, and the ferry is the part that strands people.

The east coast is the surprise. Fifteen minutes across the island there is an undeveloped Atlantic shore with a single road, a handful of beach bars and nobody on it. Rent something with wheels and it is the best half-day on the island.