This is a really strange place. One of only very few on earth, these gypsum "sand" dunes are huge and ever-changing. The National Park Service has done a great job of trying to explain how, and why, these dunes exist. They have also provided a number of great ways to "experience" them....hiking, horse back, wilderness camping, or wheel-chair accessible board walk. Oh, almost forgot: kids can "sled" down them in plastic saucers.
We visited early on a Friday morning in January and so "owned" the place. We'd recommend one stop at the visitor center first and at least see the video that does a wonderful job of explaining the what, why and how of these remarkable dunes. It only takes about 1/2 hour to do the video and see the visitor exhibits, then off to the dunes.
While there are hundreds of square miles of dunes, one can get the idea by driving the "Popsicle" loop road out from the visitor center and back (Popsicle roads go out and back with a big loop at the outer end). About half of the route is well-paved, the second half is compacted dune. Don't do this just after you washed the car! And DO plan to vacuum the car's interior after the visit...an easy job as the "sand" sucks up beautifully with a car vac.
While you can do the loop in an hour we'd recommend that you at least take a picnic...or buy some picnic stuff at the visitor's center...and spend a little time admiring the dunes. The trials are wonderful, though slightly difficult due to soft footing, but worth the effort. We didn't try camping, but would love to bring our horses (wonder what THEY would think!).
Anyway, a nice 1/2 day trip from Las Cruces...or more if with "sledding" kids!
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.