Given some of the interest shown in this subject, I'll post what I sent to John in a PM:
You might look into Colorado Springs with its Seven Falls, Garden of the Gods, Cave of the Winds, and Pike's Peak, and Manitou Springs might be worth a visit on the way to Pike's Peak. But Rocky Mountain National Park (near Estes Park, CO) is a gorgeous place to visit too, and there are campgrounds (no hookups) in the park, but also RV parks in the area. And in Estes Park itself don't skip the Stanley Hotel (built by Stanley of Stanley Steamer fame), a gorgeous place and they welcome tourists to visit.
The Georgetown Loop Railway (just off I-70 near Georgetown, CO) is a fun ride, Leadville has a small railroad and is the highest city in CO, and in the U.S. as far as I know. There are old mines in many of these areas, too. Another small railroad (along with history and casinos) can be found in Cripple Creek, just a bit above Colorado Springs. There's also Gold Camp Road, part of which is an old railroad track bed and gets you to a tunnel or two also.
Central City used to be a great place to visit, and there are still a few things there such as the Central City Opera, but casinos have ruined it and next-door Blackhawk. The Peak-to-Peak highway ( CO hwy 72) north out of Nederland (at the top of Boulder Canyon) is a very pretty drive, too.
The Great Sand Dunes National Park between Walsenburg and Alamosa, and the Cumbres & Toltec RR that runs across the border between Chama, NM and Antonito, CO, a great all day ride, are also things you might enjoy.