Up in the northeast of this vast land famed for its lush, dense rain forests and marshes, in a relatively little-known state calledMaranhão, is some 1,500 square kilometers (580 square miles) of dramatic white sand dunes - a sight made all the more impressive by the existence of lagoons between them, formed by rainwater. This Lençóis Maranhenses National Park can be visited by 4x vehicle but...  keep reading