I'll second Leadville - I spent 2 weeks during August & watched the Leadville Boom Days & the 100 mile bike race, drove many of the trails & stayed at a couple of the campgrounds around Turquoise Lake & at Camp Hale. A journal of my two weeks starts
here.A couple of other suggestions: Mesa Verde National Park is worth a visit. I really enjoyed the ranger guided Long House tour. Another favorite is the hike to
Hanging Lake near Glenwood Springs. Some photos:
Hanging Lake, CO.
For a 4 wheel adventure, drive out to the Crystal Mill & the Town of Crystal near Marble, CO.
Photos.