Night One--attend a star party at the McDonald Observatory. Do make reservations ahead of time, and try to schedule your trip when there's no full moon. We went the day after Christmas, which made the crowd pretty reasonable ("just" 400 people, compared to 1000 a few nights later!). Even with the full moon, we had some amazing views: Jupiter plus four moons, the orion nebula, and (of course) the moon in all its glory. Plus assorted star clusters. There's a cafe on the premises where you can have dinner and warm up with hot chocolate.
We stayed in tiny Fort Davis at the oldest hotel in West Texas (according to the proprietor)--a very charming B&B called The Veranda. Another option would be staying in Fort Davis state park a few miles from town. At least from the outside the Indian lodge looks delightful.
Day One--The Fort itself has been restored to its former glory, so you can see how officers lived at the end of the 19th century. You can also see the hospital, complete with instruments and explanations of medical procedures. Behind the fort there are trails up to a bluff with splendid views. Then drive back for the afternoon tour at the observatory--you'll get to see the biggest telescopes up close and learn about the research going on there (exoplanets...dark energy...wow).
Day Two--Marfa, 20 miles away, is another dust mote of a town, but (believe it or not) it's a major art mecca. Make reservations ahead of time to tour the collection of the Chinati foundation, which houses major works by Donald Judd, Dan Flavin and 10 others, in abandoned military buildings. You can't see the collection without a tour, and never fear--the tour guides maintain a low profile. They mainly just guide you around the premises and give basic information.
The town accommodates the art crowd with an appropriately elegant book store, restaurants, and the smallest NPR radio station in the country. Remember: dust mote. Marfa ain't Santa Fe. But in a way, it's better. Talk about totally quirky and unexpected.
Day Three--Now you have to visit the Chihuahua desert center, which has some lovely trails--one into a canyon, and another to a hilltop with a terrific geology exhibit.
Next question--should we open our own little bookstore in Fort Davis, since it doesn't have one? Can we? Can we? The family says No, which means we'll just have to plan another visit. There's actually much more to do--more hikes, drives, more astronomy, more art, and even more in the way of performing arts. I hear Grizzly Bear performed at The Ballroom in Marfa last year. I'm already starting to plot and scheme .... there must be a trip #2.