Colorado 2008 trip pictures from the Glenwood Canyon Trail.
The Glenwood Canyon Trail is a path about 15 miles long through the gorge of the Colorado River. Besides the river, the gorge also carries the major Chicago to San Francisco railway line, the two separate two lane (50 foot wide) roadways of Interstate 70, plus the 10 foot wide recreational path. This is a major engineering feat that took perhaps 50 years to plan and over 10 years to build. The project was NOT carried out without changing the character of the canyon, but overall it was done in a tasteful manner. For example, the road is routed through tunnels in the canyon walls for a mile or so through the most scenic section to preserve the appearance of the canyon.
The bike path is a concrete "sidewalk" ten feet wide, but it rides pretty smoothly for the most part. You do get the sidewalk joint bumps, more or less, at various parts of the route. The joints are typically 15 to 20 feet apart, rather than every 5 feet as you'll find on city streets.
The Glenwood Canyon Trail is probably the most spectacular bike path in the country (with Vail Pass or The Rio Grande Trail, see below, ranking as number 2).
With the ("Rio Grande") bike path I'm planning to ride tomorrow and the I-70 corridor bike paths, you have a more or less continuous 140 mile paved off road route from Aspen to Keystone, via Glenwood Springs, Vail and Frisco. I'd estimate that only about 15 miles are missing and these are along very low traffic roads. I actually rode from Glenwood Springs to Gypsum this day, about 50 miles round trip. The section from Gypsum to Eagle was just completed a few months ago, bypassing a section of road (US-6) that went along Eagle Airport.