The 155,000-hectare (383,000-acre) Parque Nacional Lençóis Maranhenses offers an intriguing and spectacular landscape seen nowhere else on earth -- a vast desert formed of tall, snow-white sand dunes, interwoven with beautiful pools of turquoise rainwater. The dunes are formed by the region's strong coastal winds. During the December-to-May rainy season, over 1,500mm (60 in.) of rain falls and collects in the basins between dunes forming countless blue freshwater lagoons. In June, when the water levels are at their highest, the dunes look like a giant mosaic of white interspersed with sparkling dots of blue, turquoise, and green.
Visitors can enter the park only on foot. The town of Barreirinhas, just outside the park, is the jumping-off spot for exploring the park and the surrounding region. The best season is June through September, when the rainwater lagoons are deepest, most swimmable, and most spectacular, and the weather warm and dry. By December and January, the water has all but evaporated, leaving only desert.