Manitou Springs is just outside of Colorado Springs in...Colorado. The Manitou Cliff Dwellings are located there, which are some structures built over 700 years ago by Native Americans. The structures have been "reconstructed", but I think that they were originally located in this impressive place - under the overhang of a cliff, in sort of a big cave.
What's nice is that, unlike Stonehenge, you can wander all around the site - going into the various rooms. There's a show put on by Native American dancers, that is well worth watching.
The site is not as big as you might expect, but it's definitely worth a visit.