Lençóis Maranhenses National Park, Maranhão, Brazil

Composed of large, white, sweeping dunes, at first glance Lençóis Maranhenses looks like an archetypal desert. In fact it isn't actually a desert. Lying just outside the Amazon basin, the region is subject to a regular rain season during the beginning of the year. The rains cause a peculiar phenomenon: fresh water collects in the valleys between sand dunes, spotting the desert with blue and green lagoons that reach their fullest between July and September.
The area is also surprisingly home to a variety of fish which, despite the almost complete disappearance of the lagoons during the dry season, have their eggs brought from the sea by birds.