I'll add my name to the list of people disappointed in Mt. Rushmore. Just don't get that. I will say, though, that there's a restaurant called Creekside in Keystone (right near Rushmore) that had some EXCELLENT food. Made up for the let-down at Rushmore
I think Carlsbad Caverns will surprise just about anyone if they take the natural entrance (there's two ways to get to the main cave, called the big room. One is take an elevator down, the other is to walk down via the natural entrance. ALWAYS take the natural entrance!) You just keep going down and down and every once in awhile you look up and see the entrance, which is HUGE, and you know it's huge 'cause you walked through it 20 minutes ago, but now it's a tiny little window with a tiny silhouette of a person walking along the trail.
And then even after you're out of sight of the entrance it's a good hour, filled with amazing sights, to get to the big room, which has so many amazing things that it makes the stuff you've already seen look ordinary by comparison.
It really is an incredible cave.