Holbox is a strip of sand and mangrove off the northern tip of the Yucatán in Mexico, forty kilometres long and barely two wide, and there are no cars on it. The streets are packed sand. Maya families first crossed here in the nineteenth century to get away from fighting on the mainland, and the village was founded in 1854. It lived on fishing, lobster above all, and had no mains electricity until 1987. The name is Yucatec Maya for black hole. The town now runs on bicycles, and murals cover it, big bright ones left by street artists from all over the world across shops, houses and cafés. The beach begins where the sand streets end, so you walk to it from anywhere in the village, and the water in front of the hammocks stays shin-deep for hundreds of metres and warm all year. Out at the end of the long wooden pier, under its palapa roof, the shallows turn pink and gold around you while the fishing boats drift back in.
From June the sea beyond fills with plankton and fish eggs, thick enough to bring whale sharks up to the surface to feed. One aerial survey here counted as many as 420 of them at once, the largest gathering of the species ever recorded. The boats go early, because the ride out is an hour of open water and the wind builds through the morning. Swimmers get in a few at a time rather than all together, holding the distance the guide sets. Then you are in the water beside a filter-feeder many times your own length, moving steadily along the surface with its mouth open. A launch crosses the Yalahau lagoon behind the island to Isla de los Pájaros, where flamingos, pelicans and frigatebirds crowd the mangroves, with dolphins on the way over. And on a warm moonless night, with nothing bright enough on the island to wash it out, the sea at the western tip flashes blue-green wherever it is stirred. People wade in to watch their own footsteps light up.