We took a fantastic summer vacation to Colorado for 1 week two years ago. We stayed in Downtown Denver. We went to a great bug/butterfly museum in Westminster, about 45 min north of Denver. We didn't go to Boulder, so I can't offer any ideas there. We drove about 3 hours west of Denver, stopped to see Vail, stayed in Glenwood Springs. We stayed at the Hot Springs Lodge, which was lots of fun. We rented bikes and went on a bike ride through the canyon there (a 5 year old could do this). We went on a mild white water rafting excursion. My husband did the entire trip, while a van took me with our then 3 and 5 year old girls a couple of miles down river. After the rafts got through the worst of the rapids, they pulled over and we climed in! It was great. We took a day-trip from there to Aspen. Over all, it was great. There are tons of places to stay, all the ski resorts have fun stuff in the summer too! Enjoy!