Isla Mujeres

Two very different days run out of the same small harbour. The big-animal trips leave at dawn and head well offshore, then spend hours reading the surface, birds first and fins after; the permits that govern them put only two swimmers and a guide in the water at a time, in short rotations, wearing flotation and keeping hands off. The reef days are the opposite: a hop of minutes from the harbour, two tanks, back by early afternoon, usually on small open boats with a ladder over the stern. Most people mix the two rather than choosing.

Underwater this is the northern end of the Mesoamerican reef, and it is flat country. Expect low coral heads and spur-and-groove ridges on white sand in modest depths, not walls, with the sand channels between them acting as the crossing points for rays. A mild current normally runs along the reef line, so dives are worked as gentle drifts with the boat following bubbles. Visibility swings with the weather, glassy after a settled spell and milky green once wind has been stirring the shallows for a day or two.

The sculptures were sunk deliberately, to pull diver pressure off the natural reef near Cancún, and that is still how they dive: shallow, bright and busy, with snorkel boats working overhead and figures set out in clusters you swim between. It is a photographer's site above all, wide angle and hard overhead light on a subject that holds still, and it rewards the first slot of the day before the sand is churned. A second, shallower gallery on the Cancún side is worked mainly by snorkellers. The offshore wrecks are the counterweight, deeper and darker, with more current and more structure to read.

The mix suits beginners and mixed groups where not everyone dives, since depths are modest, conditions are forgiving and there is enough shallow reef and snorkelling to keep non-divers occupied. More experienced divers tend to use the island as a base and add cenote days on the mainland or a crossing to Cozumel. Timing matters more than usual, because the two headline seasons sit at opposite ends of the calendar: April falls in the gap between them, and October and November are the wettest and windiest months of the year.