White Sands National Park in New Mexico

White Sands National Monument (U.S. National Park Service)

White Sands home page

I can't even begin to share the awe of seeing this park, it's magnificent.  My advice though is go in the fall or winter, because it was brutally hot by the time we got there and it hadn't even reached the alert stage. Spending too much time out on the dunes isn't a good idea what with the heat and then the reflected heat.  As you can see on the Link to White Sands official website there is an alert for temps 100 degrees and above. It was about 97 degrees on the day we went and I drank so much water/sports drinks I was sloshing around like a water barrel and had to keep getting in the car to cool down. 
 Oh! and WEAR a hat.