Mammoth Cave National Park, Kentucky
Mammoth Cave is as pretty as Carlsbad Caverns in New Mexico or Luray Caverns in Virginia, but it is mammoth. The area is pretty. The campground is nice. We took a long tour inside the cave and it was impressive. You can register ahead of time online. While this is not a must see, it was about 8 hours out of Pittsburgh and made a nice meaningful stop on our trip. We drove to Mammoth Cave on a Saturday and went to mass. We toured the cave on Sunday and left for Arkansas on Monday morning.