Fly into Denver.
Spend a day there, eating one dinner at the Buckhorn Exchange.
Drive up to Boulder and base yourself either in that city or nearer to Rocky Mountain National Park. The day trips in that area to places "with majestic mountains" are pretty much unlimited, and Boulder itself is a pretty neat place for young people.

Obviously, it is hard to fly into any place other than Denver. The Buckhorn Exchange is about the last place I would take a bunch of teenage boys.

Spending a day or two in Denver is fine with the different museums, could consider a Rockies game if they are in town.

I would consider basing in Frisco or Breckenridge. For there you have a number of day trip options - Mineral Trail in Leadville, several gold mines, bike trails, Alpine slide in Breck, on to Glenwood Springs and the trail along the Colorado river, lots of hiking options, hot springs in Glenwood Spring.

You have a lot of options so it is hard to define a specific trip for you. Might check out a couple of guide books for Colorado to better understand your options.

I have 2 teenage boys. I agree with the Breckinridge suggestion. RMNP is an alternative if your group is really into hiking. Breckinridge and the surrounding area will have a wider variety of things to do. Buckhorn Exchange is my sons' favorite Denver restaurant, but it is for serious carnivores. If you have any vegans in the group, go elsewhere.

fmpden,
I've flown into many placed in Colorado without it being hard?
Durango, Grand Junction, Co. Springs, Eagle County, and even Cortez. If you are flying American Airlines,it would be just as easy to fly into most of the above as it is Denver. If you are flying United, then you would have to connect. If you are going to have to connect in Houston, again no difference than flying into Denver. Plus, Denver airport has the highest car rental rates that i've ever encountered. So, if you pay a bit more to fly somewhere else, you might make up the difference on a car, is my point.

I fly into COS all the time too, it's a breeze, and much easier to get into/out (from a land side perspective) because it's a fraction the size of DIA. Cheaper car rentals are a bonus.

The boys might like the cog railway up to Pikes Peak (or you can drive), hiking in Garden of the Gods, Cave of the Winds, the Olympic Training Center, the Air Force Academy, loads to do.

A dude ranch might be fun too. Afterall, they're dudes

If I remember correctly - one thing teenage boys like is seeing cute girls - and Boulder (45? minutes from the airport) is a good place for that - plus college towns are also fun for teenagers - who are probably thinking about when they go to college.

And while I/we love Frisco - and Breckinridge and the "Summit" area (a couple hour drive from Denver) - Aspen (a couple hours further drive) - has a certain lore that might also appeal to the lads - and even the parents? http://www.aspenchamber.org/

Also - on the way - going for a soak in the big outdoor "pool" at Glenwood Springs is a fun stop. http://www.hotspringspool.com/

Also like the Colorado Springs area - having spent time there while at the AF Academy - and either driving up Pikes Peak - or as noted - taking the railway is a fun day. FYI - assuming you don't hit traffic - you can drive from Denver to the C. Springs area in an hour.

Nearby Manitou Springs (where you catch the Pikes Peak cogway) - has some cute B & B's and is fun to explore - as is the Garden of the Gods. http://www.manitouspringsgov.com/

I'd give Boulder a miss; not much for teenage boys there (plus college is in session only for summer classes), and it's not really convenient to anything. (I live there, and I know.)
I agree that Colorado Springs might be a good option; lots of attractions, and it's a gateway for the mountains. Staying in a ski mountain condo (reduced rates off season) might be a great option for you; many mountains have attractions of their own (ride the lift up, bike/hike down, do alpine slides, etc.) You could also go to the Glenwood area for the largest hot springs pool (and Glenwood Caverns Adventure Park http://glenwoodcaverns.com/glenwood-springs-cave-tours.html, or hike to Hanging Lake); a short ride away there's the Crystal River and Marble (sadly, they've closed off the hike to the quarry), or even Aspen and the Maroon Bells.

Visit a brewery - Coors in Golden, Bud in Ft. Collins. Even though they are underage, I think they will like it - my kids did at that age.

So Sylvia: I gather you are not a teenaged lad - and don't a number of lasses attend summer school?

Boulder is also home to Triathletes/bicyclists and has a number of recreational activities: http://www.bouldercoloradousa.com/things-to-do/

There could be some white water rafting at that time of year. Hiking and mountain biking come to mind as well.

I also recommend Aspen. It is gorgeous there, has lots of history and 'urban legends' like Hunter S Thompson) There is so much to do there, the boys and their parents will be happy.

Look at lodging at The Gant, which is easy walking distance into Aspen town and also has a free shuttle.

And what do you suggest these teenage boys do with these older college girls who are busy studying? Let's not be so sexist. Besides, they can look at girls anywhere. That's hardly a reason to stay somewhere.

"Boulder is also home to Triathletes/bicyclists"
I live 5 houses away from an Olympic runner, and a couple other Olympians live nearby; so what? You can bike the Boulder Creek path, or hike, or attend the CU opera; I just don't think it's the best place to stay for a gaggle of teen boys.
IMO, Colorado Springs or the mountains would be better choices.

You might also want to consider Telluride. We spent a week there this summer (prices are GREAT during non festival times) and never exhausted our activity options. Great little town! Fly into Montrose or Grand Junction.

We had our last Regis reunion - based in Boulder and loved it. We have also started the Reunion in Aspen - but we lost a couple guys up there.

Most people I know love Denver.

Shame that you live there and are so blase about it.

Flying into CO Springs or Telluride would be my choice - and no, tom I'm not a teenage boy any more than you are.

(Ignore it sylvia3. He can't help himself.)

From Denver you could connect to any of those other cities easily. If you think about Telluride, you will want to avoid the third weekend which is the Bluegrass Festival.

I know alot of the activity companies in the area and the kids would have a blast between the rock climbing (there's a Via Ferrata in Telluride), river rafting, fly fishing, hiking, biking, jeeping, etc. Also, there are some casual restaurants like Brown Dog Pizza so it's easy to grab a quick bite.

Condos are plentiful and having a kitchen would be so much easier.

For other options, you could fly from Denver to Durango for a night or two, to take the train ride to Silverton, or go to a cowboy chuck wagon dinner. This puts you in easy reach of Mesa Verde National Park for a full day of hiking and ancient Pueblo Indian sites. Then, you could go up to Telluride for the rest of your time and fly back to Denver from there.

Yes, Telluride and the San Juan mountain range are beautiful - and loved the area - but it's just a bit of a "commute" from the other attractions in Colorado

BTW - never confused either Janis or sylvia with being teen age boys - or understanding how such lads think.

Tom, the 1950s are calling you; they want their sexist mindset back.

Tomsd, to whom are you referring? "Most people I know love Denver. Shame that you live there and are so blase about it."

Willmax1 - back to your question... I suggest you make a loop connecting RMNP, Breckenridge and Colorado Springs. You can start at either COS or DEN, wherever you can get the best flight/car deal. RMNP so they can experience a western NP, Breck for slide, biking, hiking, rafting opportunities and the old west feel of the town. Colorado Springs for Melnq8's suggestions above. I would do RMNP 3 nights, Breck 4, and CS 2. If you can add a night do so to Breck for a day trip to any number of interesting places.

There are other great CO loop trips, one being Durango/Ouray/Telluride/Mesa Verde/Durango.Beautiful scenery, hiking biking, NP etc.

I would definitely include at least one ski town as they have great summer activities and endless lodging options.

Have fun, Colorado is an amazingly beautiful state.

I agree with taking in at least one ski town, b/c they have lots of fun summer activities. We've rented mountain bikes at several places (including Keystone and Breck) and a mountain scooter at Copper. My boys like the big hot springs at Glenwood Springs - they also have a mountain coaster there. We also ride at least one alpine slide when we're in the Colorado for the summer.

We've also done white water rafting and jeep tours. One year we drove ourselves - over Cinnamon Pass from Lake City, and up to Yankee Boy Basin near Ouray.

Personally, I would avoid Colorado Springs and Boulder. Neither is 'in' the mountains. They are fine basecamps for a weekend getaway, but for 8-10 days you will want to be deeper into the mountains instead of having to drive every day to get to them. At most I would use either of them as a place to stay overnight to help adjust to the altitude, then move on and go to RMNP and/or a ski town.

Well, hope Willmax1 has been gathering in the varied advice. Colorado certainly does have a lot of options to enjoy/explore.

As for renting bikes - in the summer at Vail - we enjoyed renting bikes and riding the ski lifts up the hill - and then bicycling down the mountain trails and then over to Beaver Creek. Great fun that and believe you can do that at other ski resorts also.

BTW - Newsflash for LOLs and Grad Assts: Teenage boys today still like to go places where there are girls, and Boulder certainly qualifies.

Please stop obsessively talking about college girls, it's getting creepy. OP said the boys love the outdoors and wanted an active vacation for them and their parents, not a trip where they could walk around a college town and lust after young women.

Hey - sorry to say - IMO - it's not creepy at all. Mentioned it once - and then the Boulder resident who doesn't think much of Boulder chimed in - and then of course - janis had to add her two half-a-pennys.

And then you other LOL's (formerly over-protective mothers? - have to also weigh in.

Guess it's typical of how PC some of us have become.

BTW - believe the "teenage" boys will have graduated from high school at the time of this trip. Some of us also used to call them young men.

Tom, you are really getting creepy with this reiteration of how much teen boys just want to ogle females.

I NEVER said I didn't "think much of Boulder"; I said I thought there were much better options for a bunch of teen boys.

"how PC some of us have become"

You are certainly not PC; not even close. And in this case, being PC by not being sexist is far preferable.

sylvia: Are you one of those so stuck in Academia that you just don't seem to enjoy life?

Well, this is getting interesting.

I can't imagine Boulder being that interesting for anyone really. It's a great town and is between Denver and RMNP and of course the University. But, really not somewhere I would spend a vacation, I don't think.

I always stay at the Whole Foods Store(smack dab on the HWY), when we go through there to RMNP. It's a really big WF's

Oh, one other major thing I like about Boulder. Montbell has their only Flagship store there. I like their outdoor gear much better than any other that I have found.

stay* should have read stop

"sylvia: Are you one of those so stuck in Academia that you just don't seem to enjoy life?"
What a bizarre comment. What makes you think I'm stuck in Academia, and that I don't enjoy life?
Simply bizarre.
Have yourself tested.

Yo Sprio: I know I know. Since Boulder doesn't have a slot canyon to explore - it doesn't rank with the top attractions.

Hey - I have a novel idea. Why not ask the graduating lads what they want to do? Perhaps having them read this thread will give them more input? And maybe they would like to visit the largest University in Colorado?

What planet is he on? Tomsd comments are just off the wall. Sylvia3's is pretty much on target. I have never fully understood the fascination that some people have with Boulder and Estes park. CU is a beautiful campus but not more so than many other colleges/universities in this country. And it is a college town. And Estes tends to be an over run, in the summer, tourist town with tourist oriented shops. The many more authentic old towns in Colorado. RMNP is pretty but so is many other parts of the states.

I would vote for Estes Park and RMNP. Stopping in Boulder might be ok, but I just wouldn't stay there as a base. I've never seen so many bicycles as Boulder and even on the HWY(that includes any city like Portland, San Francisco, and Seattle).

Here are a few reviews of Boulder/Colorado Univeristy, the first noting it's beautiful setting next to mountains - the next one ranks it #2 for foodies - the 3rd one - from Parents and Colleges - has it #2 also, and the 4th has this quote from Sunset magazine - with a great pic:

"If Heaven has a college town - it's probably as beautiful as Boulder".

But of course, some think otherwise. Are they perhaps trying to steer tourists away?

http://colleges.usnews.rankingsandreviews.com/best-colleges/university-of-colorado--boulder-1370/reviews

http://www.thebestcolleges.org/the-10-best-college-towns-for-true-foodies/

http://www.parentsandcolleges.com/top-ten-lists/list07-bct/

https://www.nmnathletics.com/pdf3/82852.pdf?ATCLID=1180529&SPSID=3868&SPID=256&DB_OEM_ID=600

"Well, this is getting interesting. "

Best summary of a thread I've seen in a long time.

Boulder is a great town to live in. Certainly worthy of a day or so. But there are far better towns to use as a base for an 8-10 day trip to the mountains. Steamboat, Estes Park, Breckenridge, Aspen, Vail, Durango and Telluride come to mind.

There aren't many times that teenagers can take a week long trip to the mountains with their friends, paid for by their parents. I think that in the overall scheme of life, going to the mountains and enjoying the outdoors is going to be a far better graduation present than hanging out in Boulder and checking out the women.

Put that last sentence in the 'things that shouldn't need to be said' file.

FYI - never meant they should base their whole trip in Boulder but a day or two would be great.

If I was planning the trip - I would lobby for 10 days - and assuming flying into Denver - then would start off with a night in Denver - and then get out to see the state.

Boulder is close - and good for a night or two (if you arrive later in the day - maybe two nights) - then a couple nights in RMNP - and/or two or three nights at the Summit (Frisco/Breckinridge).

Then - choose to then perhaps add Aspen or if you want to see more of the state - drive down the middle (beautiful drive from Breckinridge to Colorado Springs) and check that out - possibly staying at Manitou Springs for a few days.

From there - it's an easy trip up Pikes Peak (cog railway or drive) - and a visit to the nearby Garden of the Gods (maybe walking/hiking around there)- and also close to downtown C. Springs and also the AF Academy.

From there - you are within an hour plus of the Denver airport - but not during afternoon rush hour.

There are of course - other ways to do it, staying longer in one place - but if you have an energetic group - I think they might like to get around and see a fair amount of beautiful Colorado.

With all the people in your travel group, I would not want to be changing hotels too many times.

I also would not suggest CO Springs (not a mountain town) or the Air Force Academy (I can see the teens yawning now!).
I suggest you focus on the Colorado outdoors and activities, per your OP.

Again, I recommend Aspen, with maybe a stop on the way there and back, like in Georgetown, Vail, Glenwood Springs for lunch or an overnight.

Drive another route back to Denver from Aspen, over incredible Independence Pass.

Fly in and out of Denver. Stay the first night in Boulder, if you want to acclimate. It is a cool town, and HS grads might be interested in seeing the gorgeous campus. We have toured many, many campuses, and we think CU-Boulder is tops for setting and architecture.

Aspen is beautiful, and it is a special place to visit for a special graduation trip. Go to their website to see what events are happening. They have lots of outdoor music festivals, for example.

Look what's happening in Aspen in June, for the adults in your group:

JUNE
Jun 14 - 16 FOOD & WINE Classic in Aspen