Try a late spring or early fall trip on the old Route 66. My daughter and I did that a couple of years ago and it was one of our most memorable trips ever. It takes you through or close to a ton of National Parks and Monuments and some spectacular western scenery. History is over every hill.
Make sure to stop at the Midpoint Cafe in Adrian, Texas. As they like to say, "When you are here, you are halfway there!" It's 1139 miles from the start of old 66 in Chicago and 1139 miles to its endpoint in Santa Monica, CA.