Mine is a pretty easy 8 miles one way, starts on residential and county roads in the Gunbarrel area of Boulder County, swing north of the tiny muni airport, then onto MUP's (Cottonwood, Foothills, Boulder Creek), popping out near the University of CO, then on surface streets which for the most part have bike lanes. The only tricky part is an underpass under US36 that doesn't have a bike lane; it does have a sidewalk that people use, but there isn't a smooth way across westbound. The low point is about halfway (the run along Boulder Creek), so I get moderate climbs at the end both directions. The MUPs are pretty busy, especially in the mornings with dogwalkers; many people with multiple dogs that tend to cover the entire path. Only a problem when you encounter them at a curve.