Don't forget the Corn Palace in Mitchell, and Wall Drug. Of course, the Badlands and Black Hills. Also, the only single-syllable state capital in the U.S.
Well, duh! We always missed the Corn Palace, but we did camp right next door to Laura Ingalls "The Long Winter" house.
And driving thru the Black Hills, and possibly defacing federal property by spray painting "Wolverines #Spartans Will" on a certain rock...