Tulum

A walled port town whose cliff drops to a small beach below. The gate opens at eight, and with no shade on the site that is the hour to arrive.

A collapsed limestone sinkhole holding water clear right down to the floor. Turtles swim in it and bats hang from the roof of the cave.

Two flooded caves connect underground, and divers with certification go through. A snorkeller can still see as far as the first chamber.

Mangrove and lagoon run together in this reserve, crossed along a channel cut in Maya times. In a life jacket you let the current carry you for about half an hour.

Forty five minutes inland, a site in the jungle where bicycles carry you between the structures. An old causeway has been traced running straight for 100km to another city.

Accommodation and kitchens line one narrow road best travelled by bicycle. There is no street lighting after dark, so a torch or a bike lamp is needed.

Green turtles come into this shallow bay to feed on seagrass, and entry is with a guide. Touching them is forbidden and the rule is watched.

A small site at the entrance to the reserve with few visitors. A boardwalk runs from the ruins straight out to the lagoon.

Three holes in the roof are jumped through to get in. A ladder is there as well, and the water is deep enough that your feet find nothing.

Town, beach and ruins each sit about fifteen minutes apart by bicycle. A cycle lane runs beside the road, and the daily hire rate is low.

A natural inlet some 15 minutes north of Tulum where underground rivers meet the sea, mixing fresh and salt water. The ticket covers food and snorkel gear, so people stay all day. Where the waters meet, a shimmering layer wavers like heat haze.

An open cenote on the Coba road, named because taxi drivers once washed their cars in it. Water lilies float on top, and beneath the rocks an entrance leads cave divers into the passages. Crowds here stay thinner than at the famous cenotes.

A cenote on the Tankah coast north of Tulum whose channel through the mangroves connects underground to the sea. Cool fresh water layers over warm seawater, and you feel the temperature shift as you swim. Shallow enough that snorkelling is all you need.

A shallow jade lagoon south of Tulum with a deep sinkhole at its heart, showing as a dark navy circle. A wooden pier leads in, swimming is allowed only in the shallows, and a rope closes off the deep part. The water barely ripples, good for children.

A fishing hamlet where the dirt road through the Sian Kaan reserve finally runs out. The jolting drive from Tulum takes hours, so few make it. Boats go out for fly fishing and dolphin spotting, and the village kitchens cook the day's lobster.

White sand running south from right below the Tulum ruins, its palms leaning toward the sea. Many walk down after the ruins for a swim. Each beach club charges separately for loungers, so ask before sitting.

About 30m down, a hydrogen sulphide layer spreads like a hazy cloud with branches poking up through it, giving the look of a river under the water. Because of the depth only experienced divers go in. Snorkellers will see nothing.

A protected beach where sea turtles nest, and no hotel may be built. A small entry fee gets you in, and a little cenote hides in the woods at the far end. In nesting season the nest zone is closed at night.

A long lagoon about three hours' drive south, said to show seven colours depending on depth. Stromatolites thousands of years old grow along its shores and must not be stepped on. To protect the water, many spots forbid sunscreen.