Bacalar — the Lagoon of Seven Colours

The Bacalar lagoon stretches some forty kilometres south of the Riviera Maya, close to the Belize border. Its fame rests on a rare optical effect: depending on the depth, the nature of the bottom and the angle of the sun, the water shifts through seven shades of blue, from milky turquoise to an almost black indigo.

You sail aboard a boat licensed to operate on the lagoon, with an electric or four-stroke engine, in line with the local environmental charter. The route takes in the pirates' channel with its white sandy bottom, the stromatolite zone — living formations thousands of years old — and one of the deep cenotes dotted across the water. Swimming stops are built in at every notable stop. The outing runs every day except Wednesday, in English and Spanish. Allow two and a half hours' drive from Tulum, three and a half from Playa del Carmen and four and a half from Cancún, which makes leaving from Cancún uncomfortably long. The programme covers an hour and a half on the lagoon, Bird Island and the pirate channel, a swim at Cenote Azul, a viewpoint stop on the square by Fort San Felipe and around twenty minutes free in the centre. The à la carte meal is included; drinks and entry to the fortress museum are not.