Lençóis Maranhenses is 1,550 square kilometres of white dunes on the coast of Maranhão, in northeastern Brazil, and it is not a desert. It takes more rain in a year than a desert takes in several. The rain falls from January to June and the sand drinks it, until the water table sits higher than the valley floors between the dunes and every hollow fills. By about June the lagoons are at their fullest, thousands of them, up to three metres deep. It is clear rainwater over pale sand, warm at the shallow edges and startlingly cold where it drops away. Then the sun takes them back at roughly a metre a month, and by the end of the year the valleys are bone-white again. Deep inside the field two lagoons never dry at all, and the only permanent settlements sit beside them. A few dozen people live there, with no road in and hours of walking across open sand to reach them.
There are no paths and no landmarks, so you go with a guide who reads the shape of the dunes to get from one lagoon to the next, barefoot over warm sand. You push up the soft face of a forty-metre dune, sinking to your ankles with every step. From the crest the pattern finally shows itself: white ridges running to the horizon with a blue lake cupped in nearly every hollow. Then you go down and swim, and climb the next. Late in the day the sand turns orange and pink, the shadows stretch out long and blue between the dunes, and the lake below goes glassy and doubles the sky. Past the last of them the sand continues, no plant, no sound, no mark in any direction. And there are fish in water that disappears every year. Some arrive through channels from the rivers when the rains come. The wolf fish never leaves at all: it burrows into the damp mud and waits out the dry months, while the small jacundá lays eggs in the sand that hatch when the water returns.