A 1550 square kilometre national park with vast expanses of dunes, which look like bedsheets stretch 70 kilometres along the coast and up to 50 kilometres inland. Located halfway between São Luís and Piauí, it's a spectacular place from about May to September when rain filtered through the sand forms thousands of crystal-clear pools and lakes between the dunes. The lagoons are at their best in June, July and August. The park also includes beaches, mangroves and some interesting fauna, especially turtles and migratory birds.