Riviera Maya, one road along the reef

The Riviera Maya is the stretch of Quintana Roo coast running south from Puerto Morelos to the edge of the Sian Ka'an biosphere reserve: roughly a hundred and thirty kilometres of white sand, low jungle and one straight federal highway, the 307, tying the whole thing together. Almost everyone lands at Cancún, and Cancún is the coast at its most engineered, a barrier island of hotels with open Caribbean on one side and the Nichupté lagoon on the other, and ferries to Isla Mujeres leaving from the mainland docks. An hour south, Playa del Carmen is denser and walkable, built either side of the pedestrian Quinta Avenida, and it is the port for Cozumel, whose drop-offs are the best known diving in the country. Another hour on, Tulum keeps a walled Maya city on a cliff above the sea and a beach road heading down towards the reserve. What ties the three together is limestone. There are no rivers here at all; rain sinks through the rock, travels underground and surfaces in cenotes such as Dos Ojos, Gran Cenote, Cristalino and Azul, where you swim in cold fresh water under stalactites minutes after leaving the sea. Offshore lies the Mesoamerican Barrier Reef, the second longest in the world, protected as a national park at Puerto Morelos and shallow enough there to snorkel from a small boat. Green turtles graze the seagrass at Akumal through the summer. The dry season, roughly November to April, brings the clearest water; sargassum can reach the Caribbean-facing beaches between spring and autumn and shifts week by week. Use the coast as a base and the interior opens up easily for a day: Cobá, Valladolid, Chichén Itzá and Ek Balam are all within reach of the same highway.