Located within the Cuatrociénegas Reserve, these blinding-white gypsum sand dunes – the second largest in North America – contrast superbly with the six rocky mountain ranges that ring the valley. To visit you’ll need your own transportation and a guide. (The gate to the dunes is locked and only guides have access to the key.) A licensed guide can be hired at the Poza Azul Visitors Center. The dunes are located 18km southwest of town, at the end of a sand road.