Dunes and lagoons of "Lençóis Maranhenses National Park" in Brazil. Composed of large, white, sweeping dunes, at first glance Lençóis Maranhenses looks like an archetypal desert. Actualy it isn't 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: freshwater collects in the valleys between sand dunes, spotting the desert with blue and green lagoons that reach their fullest between July and September.