Pikes Peak, Colorado Springs, CO
Rocky Mountain National Park , NW of Denver, CO.
Bandolera National Park just outside of Las Alamos, NM. You can then stop and see the Museum at the National Laboratory.
Great Sand Dunes National Park near Alamosa, CO.
Mesa Verde National Park near Cortez, CO. Also close to four corners monument.
Durango Silverton railroad, Durango, CO.
Highway 550 from Durango, CO to Ouray, CO. is an amazing drive.
Depending on how much time you have you can do mutiple as several of these are all in the same gereral area.