We stopped at the visitor center and they recommended we visit this museum. We were glad we did. They have a large property with several exhibits to see. We bought some postcards in the gift shop as well. The indoor museum covers the timeline from prehistoric to modern times. Quite a bit of history on the Hoover/Boulder Dam since Boulder City is the town that built the Dam.
Outside they have some desert gardens (which we didn't walk through due to the heat), a locomotive you can look at from outside, and train caboose and rail car that you can walk through. There are also some old structures and equipment from the 1800s to walk through that show times in the old west.
They brought some old buildings over from other locations to set up "Heritage Street" with residences, a chapel, and other buildings. It was fun to walk through and see the mannequins on display as people who may have lived back in those times. There was even an old airstream mobile home to demonstrate how small some homes were.
Definitely worth the money ($2 per adult) to make the stop.