Instead of having a big rotunda, the North Dakota State Capitol is a skyscraper, containing 19 floors and about 80% usable space.
Built in the 1930's, it features several kinds of wood and stone from around the world.
Tour guides and capitol staff are friendly, and the free tour ends at the top-floor observation area. From there, you can choose to ride down in the elevator or let your kids convince you to take the stairs. (I recommend the elevator.)
Parking is free and close by, and the North Dakota Heritage Center museum is right next door.