What are the "must see, must do " things in COlorado?
Wife and I enjoy outdoor stuff. Renting ATV's or maybe renting a Jeep to do some offroading / exploring.
There are so many places it's hard to recommend something.
But my family used to vacation in the Colo. Springs area in the early 70's and there are some wonderful tourist/vacation spots there. We would also go up to Denver. The "outdoors" stuff isn't quite as nice, IMHO, but it has some pretty nice "big city" things to do, museums, zoo, etc.
The middle park area of Breckenridge, Fairplay and south is a wonderful place to, I'm sure. I've only passed through it once 20+ yrs ago. I think this area personifies what people picture Colo. to be. High country pastures and meadows with higher snow capped peaks in the back ground.
Further north the Estes Park area with Rocky Mountain National Park is a great outdoors getaway spot. But I've never been there.
My favorite vacation spot is Ouray, in the southwest corner. It's pronounce "YOU ray". An old gold mining town nestled amongst high peaks. It's often called "Little Switzerland". For a little town of around 600 people they have 3 or 4 or 5 Jeep rental places. Rent a Jeep and explore the high country on your own. Or take one of there tours. My best friend is from there and has two brothers that live there. One of them bulldozes the snow off Imogene Pass. This is the pass that takes you over the mountains to Telluride. Better be an experienced 4wheeler for it though, it's a tough pass. But there is some breathtaking areas around Ouray. Yankeeboy Basin is phenomenal.
You can do whitewater rafting in the Glenwood Canyon and Asspain is just another 45min. up the road. Glenwood Springs is home of the largest naturally heat hot springs pool in the country. But I prefer the hot springs pool in Ouray.
I do think you'll have a good time where ever you go, but if you drop into the Glenwood Springs area give me a shout. I live just down the road.
What time of year?
Currently, the rafting on the Arkansas and Colorado is still decent, but flows are dropping some.
Any of the mountain towns have 4wd/atv trails to explore.....some try to get between cities without touching pavement.
Hot springs are plentiful along the central part of the state.
Bag a 14'er....a few are pretty easy. If nothing else drive or take the cog to Pikes Peak.
Lots of museums especially for mining, western history, etc.
You can see alpine meadows at daylight and desert landscapes at sundown of the same day.
The dunes are worth a daytrip.
Indian ruins are pretty neat
In the winter you have skiing (all levels) x-country, snowshoeing, dog sleds, snowmobiles, snowcat tours, etc.
I'm thinking May / June.
Before it gets hot, but after the snows are done.
I have to check annual temps to know when for sure.
May is often too early, but by the 20th of June most high country roads are passable. Above 10,000 feet, mid 80's are rare. By late June, rivers are running strong for great rafting. Depending on the snow, a few areas will still be open for downhill skiing.
lotsa critters to see too. That is prime elk calving season so you can see some large herds (bulls have shed). Coyotes will be thick looking for newborns.
May or June are great times to be here in the Headwaters of Adventure, Chaffee County, Colorado.
The annual Caddis fly hatch hits the Arkansas river around Mother's Day and can be biblical in proportion for the fly fisherman.
June is typically when the commercial rafting companies are fully staffed and geared up for the spring run-off.
Chaffee county has more mountains over 14,000 feet than any other county in the state. There are ATV and Jeep rentals available for exploring the area's ghost towns and local outfitters provide trail rides and pack trips. Something like 83% of the land here is Nat'l. Forest or BLM. Lots of room to play.
Salida's downtown area is the largest nat'l historic district in the state with about 2 dozen art galleries and antique stores in this town of about 6500 residents. I'm not a big 'artsy' kinda guy but there's some real talent in town.
We have several hot springs pools and the Royal Gorge is less than an hour's drive away. Lots of motels & campgrounds available, here, as well.
However...IMHO...we have the best kept secret in the state for the shooting sports enthusiast...a (free) public range for the handgunner, trapshooter and long range rifle guys. Ranges out to 1000 yards with views to match. I've mentioned it at least a couple times on this and other boards but the 'front range' guys seem to think its too far to drive...and that's OK. But if you're headed to this area, don't forget to bring the toys. I'd be happy to give ya' the nickel tour of the place.