Created by winds that sweep the San Luis Valley floor, the enormous sand dunes that form the heart of Great Sand Dunes National Park and Preserve are an improbable, unforgettable sight. The dunes, as curvaceous as Rubens's nudes, stretch for more than 30 square miles. Because they're made of sand, the dunes' very existence seem tenuous, as if they might blow away before your eyes, yet they're solid enough to have withstood 440,000 years of Mother Nature—and the modern stress of hikers and saucer-riding thrill seekers.
- Dune climbing Trek through the 30 square miles of main dunes in this landlocked dune field.
- Unrivaled diversity You can see eight completely different life zones in this park, ranging from salty wetlands and lush forests to parched sand sheet and frozen alpine peaks, all in a single day.
- Bounty of bison Take a ride around the west end of the park, where more than 2,000 bison roam in the grasslands and wetlands.
- Aspens in autumn Take a hike—or, if you've got a high-clearance four-wheel-drive vehicle and good driving skills, take the rough road—up to Medano Pass during fall foliage season when the aspens turn gold.
- Vigorous hikes Pack a picnic lunch and climb up to High Dune, followed by the more strenuous stretch over to Star Dune. Or tackle the dramatic Music Pass Trail, which takes you to the tree line and covers 3.5 miles (and 2,000 feet in elevation change) each way.