Boulder was the fact that it is a major bike city. Nationally recognized as 'the fittest city in the nation', there are bike lanes throughout the city, and everywhere is connected by trail. Stefan had a good time, I think, just looking up where we'd go on our bikes when we got there. Although we only had 5 days of vacation, and two of them were driving, we had plenty of time to make multiple bike treks in the mountains.
The key is to not hesitate and keep your momentum uphill....it's much easier said than done, especially when you get to a very rocky patch you have no idea how to climb with a bike going faster than you'd like!
This is a nice little rest spot over a bridge on the easy Canyon trail that follows the highway back into Boulder, I believe about 20 miles outside of town. The first day we did 3 mile loop at Betasso Preserve (clockwise) and the next day we did 16 mile trek Marshall Mesa. Both were considered "easy/moderate" trails and in 19 miles I: fell 3 times, landed 6 amazing bad bruises/cuts, cried a few angry tears, threw my bike, had amazing workouts, and walked about 1.5 miles. All in all it was a fun trip, though if you saw my pictures of where I fell you'd think I was insane.
Moral of the story: We LOVE to be outside in the mountains and we love to be active. I had fun on my trip and I think I earned every single morsel of food that I ate...and I haven't even told you about our hikes yet!