Where can you find beaches and foot high waves a thousand miles from any coast? In Great Sand Dunes National Park! Due to reliable windy conditions at the base of the Rockies here and a river that runs through them, sand dunes hundreds of feet tall have formed in this area over thousands of years. The dues themselves are very strange to look at in this mountainous landscape, and even more interesting to hike through. When you visit, try hiking Star Dune (the tallest in the park). But really, any of the dunes are fun hikes, though remember that hiking through sand is not like hiking on a hard surface. The 3.5 miles to Star Dune and back is a long hike! Also, don't neglect the other parts of the park - check out the Mosca Pass trail and any of the others in what the "Preserve" section of the park. A 4-wheel drive vehicle is helpful for accessing these parts of the park.
As for hiking, there are not that many hikes in BCGNP that don't go down to the river. We did the Warner Point Nature trail and the Oak Flat Loop. The Warner Point trail is an easy 2 miles along a ridge with good views to both sides to a lookout down the canyon. It's nice, especially at sunset. We also hiked the short Oak Flat Loop, which the parks bills as strenuous. We found it neither flat nor strenuous, though there were some Gambel Oak bushes. It was also a bit underwhelming - you'll get much better views from the lookouts along the main road.