One of your first stops should be Yellowtail Dam Visitor Center. Here, you'll be able to orient yourself and pick up some great ideas before you set out exploring.
You'll have no end of sightseeing choices when visiting Fort Smith. Yellowtail Dam Visitor Center is a great place to begin here, but there are lots of other interesting spots to enjoy. Bighorn Trout Shop, and Yellowtail Dam Marina are near the tourist information center and will round out your day nicely.