Great Sand Dunes National Park, Colorado

Beautifully set against the Rocky 

Mountains, the Great Sand Dunes of Colorado (the largest such dunes in North America) are like something from another planet. It takes hours to climb to the top of the dunes from the parking lot, but the feeling of standing alone thousands of feet in the air is well worth the trek. After taking in the vistas, descend by foot or by sled/sand board and cool off in the Medano Creek at the bottom of the peaks.