Mesa Verde, Colorado
The Pueblo ruins in Mesa Verde National Park, Colorado, date back well over 1,000 years. Now preserved as part of the 200-square-mile park, the area contains some of the best examples of ancient dwellings in the United States. They are accessible only as part of a ranger-guided tour, which helps keep these villages surprisingly intact.
The park also has museums and trails, rounding out an educational experience for visitors who want to see history firsthand.