White Sands was recently promoted to a National Park; formerly it was a National Monument. We visited it in 2018, along with nearby Carlsbad Caverns NP and Guadalupe Mountains NP. It makes sense to do all three.
White Sands is beautiful and interesting, but for me a day was enough to feel I’d seen it well. Things to do include a few hiking trails and an easy boardwalk, and we also saw several families using plastic sleds on the dunes. If you bring kids, they’ll probably enjoy sledding more than hiking here.
The sands are wide and extensive, and people can get lost, to their great peril. Staying on the trails (marked with upright colored poles) is a must. We did the Backcountry Camping Trail, two miles of dazzling whiteness without much variation. Walking up steep sand dunes is more difficult than a similar climb on regular ground, and the two miles felt like much more. (It would be even more difficult on a hot day. There is no shade anywhere.) As the trail name suggests, there are small campsites in a few of the dune valleys.
We also did the Dune Life Nature Trail, which features more vegetation and a lot of child-focused educational signs about wildlife one might see. We didn’t see much wildlife, but the sand preserves footprints and trails well and we saw evidence of birds (turkeys?), lizards and snakes. Dune Life also has a few rocky vistas with steep drops. It felt more dramatic than the Backcountry trail.
The sands in this park are gypsum rather than silica, and the trail literature says that gypsum stays cool in the sun and you can walk barefooted. I was skeptical of this claim, but it’s true. We found rubber sandals to be the most effective footwear here. Whatever you wear, you’ll end up having sand in it.
Final advice: wear sunglasses. It’s really bright on the dunes.