What activities would you recommend doing, and what places would you recommend driving to or seeing in Colorado in the summer?

Would you recommend Winter Park as a central place to stay for enjoying the various activities?

We all like interesting things--2 adults & 2 girls, ages 9 & 13. A train ride, interesting scenery, climbing on rocks, kayaking/canoeing/rafting/floating, seeing the mts, etc.

Your list of activities sounds very good. I'm not familiar with all your options from Winter Park. You can do everything on your list in Durango, and several other areas. (I just mention Durango because I'm most familiar with it.) There is so much to do, that you might just want to concentrate on one part of the state, or plan a road trip with 2 or 3 stops.

Places I've enjoyed in Colorado are Rocky Mountain National Park, the Leadville area, the loop from Durango to Ouray to Telluride, Mesa Verde, Grand Mesa, and the area around Wolf Creek Pass. I haven't spent any time in Steamboat Springs and Glenwood Springs, but they're also on my must do list.

I'm not super familiar with all that Winter Park has to offer-but it is
A. BEAUTIFUL
B. Right next to Grand lake, which is amazing, and would work for some of your water sports
C. Only about 2 hours from Denver
D. Great hiking. I beleive you can take the gondola to the top of the mountain and there are tons of trails for hiking and mtn biking.
Surely there are others who can elaborate.

considering the list of things you want to do I would recomend the area southwest of denver to Durango.
Durango has the most popular train ride but Georgetown also has a neat one.You can raft the Arkansas River from Salida area. I would recomend Glenwood Springs for a night or two.
This area realy has a high concentration of things to do and see.

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You cant go wrong with a few days in Colorado Springs also.

Just got back from skiing WP (first time there). While we had a great time, I'm not sure it would be one of my first Summer choices in Co. Based on my 10-12 Winter trips to various ski areas, I would probably look at Summit County or Vail for Summer recreation. Breckenridge and Vail would be my two choices. WP was pretty small and not much to do other than ski/snowmobile/etc. While all that is great during the winter, I'm not sure it would offer a lot in the Summer? However, on a positive note, I did read where WP has a very extensive mountain bike trail system. Don't get me wrong, WP was nice...just wouldn't be my first choice.

Agree with Pumpy, WP does have great Mtn Biking, but I do not think it would be enough to keep you busy. Vail, Keystone Breckenridge all offer many actvities to keep everyone busy