Big Bend Museum, Big Bend National Park
Do not miss this nice little museum if you go to Alpine. It features explanatory panels and objects on the history and geology, fauna, flora of the region. When I went, it also had a very interesting exhibition of paintings of the Big Bend by Texan artists.
Finally, you have to go through the cactus garden in front of the museum: it is a fantastic introduction to plants of the Big Bend, very well done, and very pretty.
The museum is free.