Within a grand traditional Minangkabau-style building is this excellent museum offering a thorough overview of Padang culture. Captions are all in English, and cover Minangkabau lifestyle and architecture, as well as the Mentawais; try to visit before you go to the islands if you're heading there. There's also a rather sobering display on the natural disasters that have impacted Padang over the years.
Adityawarman Museum
Padang