It depends on how far you wish to travel out from Denver. There are a lot of mountain choices. Colorado Springs about 70 miles south of Denver has Garden of the Gods with some spectacular sights. Boulder (45 miles west) is a beautiful college town (Univ. of Colo.) and butts up against the base of the Rockies. Lots of activities there. To travel further afield, head up through Evergreen on 285 over Kenosha pass into South Park and then down to Gunnison and Montrose to see the Black Canyon of the Gunnison National Park. Amazingly beautiful but for me (who is terribly afraid of heights) there is the combined powerful attraction and repulsion at the same time of seeing the views. To travel even further, head to Aspen and to the famous Maroon Bells, or down over the million dollar highway (or Wolf Creek Pass) into Durango and Silverton areas.

I recommend starting in Glenwood Springs and the surrounding area. It's only three hours from Denver. You don't need a water park when you have the Roaring Fork River on a raft!

The Glenwood Caverns Adventure Park is accessed by a gondola up the mountain where they have cave tours, zip line, etc:
http://glenwoodcaverns.com/ Also lots of hiking/bike trails around town. You could easily spend two or three days there.

I would also recommend the Black Canyon of the Gunnison. That's an amazing spot, and up the road toward Gunnison you could check out the Blue Mesa Reservoir with marinas, boat rentals fishing, camping. From there you're pretty close to Crested Butte which is beautiful in the summer.

Then you could head back toward Denver via historic Leadville, and back up to I-70.

There are so many great places to see - it's great that you have a week which guarantees you enough time to enjoy it.

Thanks for the suggestions to get us started. I don't think we'd want to drive more than about 3.5 hours in a day, and ideally less. Maybe we'd do best picking 2-3 key areas and doing day drives/trips. How about recommendations for places to stay?

Unfortunately you need to spend some time with guide books and travel DVDs to see what appeals. There are a lot options depending on what you would like to see and do. Denver is worth a day or two.

White water rafting at that time of year could be finished because our snow pack so far this year is below average. May still find a float trip or two but the white water is pretty low by August even in good years.

Whether or not you want to do Glenwood, it WOULD get you to the possible furthest point, with a wonderful day of scenery--and it is easily within your parameter.
Colorado is a wonderland of things to do.
Don't overlook a day or so in Denver on the front or back--a Rockies game if you don't have MLB where you are.
How about fly fishing? A day on a river?

For waterparks, there is WaterWorld in a northern suburb of Denver. There is zip lining just west of Denver off of I 70 I think at the Idaho Springs exit. You can also hike on Mount Evans from that exit. Fantastic scenery.

Agree with posters above about Glenwood. My teens enjoyed the hot springs pool, the uphill hike to Bridal Veil Falls off of I 70, biking the great trails there and seeing Doc Hollidays grave at the cemetery outside of Glenwood.

Some smaller rivers have shorter raft seasons, but I recommended it because I know they still run at that time.

And be sure to stop at the exhibit along I70 that shows how that highway was built. There is a bicycle path along there also.

If you did decide to go for it one day - and drove over to Glenwood Springs - an hour or so further is beautiful/historic Aspen. Well worth the additional hour's scenic drive IMO - as is walking around Aspen, maybe having lunch, etc. http://www.aspenchamber.org/

I would go to Rocky Mountain National Park for at least part of your stay.

another place our family enjoyed was the Mt Princeton Hot Springs resort near Buena Vista and Salida. We only stayed overnight but would consider a longer stay another time. We drove there from Frisco, via Leadville and looped back east to Manitou Springs/Colorado Springs. We enjoyed the beautiful scenery along the Arkansas River. The resort is good for outdoor activities (horseback riding, biking,hiking, rafting, tennis) and the Collegiate range setting is spectacular. The resort has cabins for rent but we stayed in one of the "cliff side" rooms. We ate in the dining room there, which was fine. Some of the hot springs were closed when we visited in late May due to spring run off but we all enjoyed soaking in the main pools.

Rocky Mountain National Park for sure! You'll have plenty of hiking to choose from, white water rafting, horseback riding, jeep tours, etc.

http://www.rockymountainhikingtrails.com/

If you stay in Estes Park you'll have tons of options for lodging, restaurants, etc. We've stayed at Woodlands on Fall River several times which is condo style lodging with full kitchens just outside of downtown along the river.

Mountain Whitewater Descents offers whitewater rafting:

www.mountainwhitewaterdescents.com

SK Horses has horseback riding stables in two locations:

http://www.skhorses.com/

There's so many activities in and around RMNP!

And for

I would split my time between RMNP and Breckenridge. Breckenridge has tons of biking, hiking, an alpine slide, and cute town.

I'll make another bid for Glenwood for a day. come back to Breckenridge for a couple or 3 and then return to the Denver area by accessing RMNP from the west side to go to Estes Park.

Agree with the suggestions of RMNP and Glenwood Springs. Another option not much past Glenwood Springs is Grand Mesa. Grand Mesa offers amazing views from 'flat-top' mountains. Several choices for lodging. We stayed at Alexander Lake Lodge for 3 nights last year and loved it. No cell service, no wifi and no TV - parents loved it, kids mostly tolerated it. Lots of hiking and fishing in the area. Also agree Aspen is worth at least a day - take a gondola ride to the top where you can have lunch, check out the shops of the town.

I second Glenwood Springs and Breckenridge. On the way, maybe stop at Silverthorne for outlet shopping if that interests you (actually has decent stores). Near GS hike the up to the hanging lake, which is a great hike and awesome payoff.

Breckenridge for mountain biking and more alpine roller coaster fun, plus good eats and views.

So many helpful suggestions, thanks!! Any recommended lodging in Glenwood or Breckenridge?

Breckenridge is a ski resort town with hundreds of condos, hotel rooms, etc. Use VRBO, trip advisor, or similar search engines. IMO, they all about the same except for location.

Glenwood Springs is more of a standard down. Both the Colorado and Denver hotels are old, Victorian style hotels that are interesting. The Denver hotel is across the street from the hot spring pool. Again, try trip advisor.

Standard town. Do wish we had an edit button.

I live in northern Co and my favorite summer places are Steamboat Springs, Crested Butte, Breckenridge, Glenwood Springs. SW CO is wonderful but probably farther than you want to drive.

We stayed at the Hampton Inn in G-springs. Nothing too exciting, but you can walk to the gondola to the adventure park.

We popped into the Denver, and I might take a closer look at that, next time (more central and great brewpub in/nearby).

The Hotel Colorado is historic and worth a visit, but has mixed reviews.

In Breck, what fmpden said. We personally like being within easy walking distance of the main downtown area for shopping and food.

since you mentioned Zipline. The best zipline on the planet with one of the best train rides is the combo @ www.soaringcolorado.com Expensive, but worth every cent.

Mesa Verde is nearby and is very neat to see.