Lewis and Clark Caverns are well worth it!! Been there a couple of times and it's a great experience! The laser show at Crazy Horse is also worth it! And while you're there, check out the closing ceremony at Mt. Rushmore...
That's the only 2 we've been to, but the list looks pretty cool!
Camped 2016 (Days/Nights) - 32/23
Nights camped 2015 - 29
TT: 2013 26' Revere TBQB
TV: 2014 GMC Sierra 1500 Z71 4x4