After visiting my Dad's hometown (Grandpa Redd) we explored the Indian ruins at Mesa Verde. My dad took trips here as a boy and loved exploring, too.
Mesa Verde is located in Colorado. To get there from Utah we went through a tunnel. David really liked that and talked about it for weeks after we returned home from our vacation.
There were hundreds of ancient Indian dwellings set in the side of the sandstone cliffs. The ruins open to the public include only a small portion of the overall dwellings found at Mesa Verde. It was quite amazing to think about how they must have climbed down from the canyon top to their home in the cliff face.