Get out of the city entirely! The East Boulder Trail, a crushed gravel trail running through county lands near 95th St north and south of Valmont Rd, takes you on a tour of Teller Farm, gravel ponds, and the White Cliffs. You can take a flat ride through the farm, or climb hills by the cliffs.
A complete description is available in Boulder Urban Trails.
A short distance from there at 50th & Quaker, you can catch the Fairmount Trail, a dirt-and-gravel trail skirting the base of North Table Mountain. You're more likely to see horses than other bikes! Plus, you can connect to the Ralston Creek/Arvada Reservoir Trail, which will return to Clear Creek for a 30-mile loop.
A complete description is available in Jefferson County Central Urban Trails.
The Platte River/Adams County stretch. From Franklin & Race, it heads out of the city, following the meandering river by reclaimed ponds and small parks. This concrete trail has recently been extended a mile to 104th Ave. Watching the sun set over the Rockies is a particular delight from this path!
A complete description is available in Adams County Urban Trails and Take A Bike!
Head a bit further west, to the Walnut Creek trail. From 108th & Simms, this crushed-gravel trail runs beside a golf course and behind a neighborhood rec center. A very short on-street stretch connects to another segment that is being extended, and will eventually connect to Big Dry Creek south of Church Ranch Rd.
A complete description is available in Westminster Urban Trails.
... some of the gulch trails branching from them offer a lot. In Littleton, the Lee Gulch Trail runs between the river, the canal, and C470. This trail, part crushed gravel and part paved, offers a relaxed outing in the midst of the suburbs. In the fall, apple trees lining the trail bend low with fruit.
A complete description is available in Denver/Platte Triangle Urban Trails.
From Bar Triple-C Park, the Sulphur Gulch Trail heads east up a side draw. This concrete trail slowly gains elevation as it runs four miles through the middle of Parker. For the most part, a wide open-space buffer surrounding the creek keeps you a distance from back yards.
A complete description is available in Douglas County Central Urban Trails.
Paved trails running through Spring & Marcy Gulches are a great antidote when the rat race runs you down. Passing parks and accessing open spaces, these two trails are connected downstream at Redstone Community Park (Town Center & Foothills Canyon). A short ride on along the dirt Foothills Trail connects the upstream ends for a loop trip.
A complete description is available in Highlands Ranch Area Urban Trails.
The Highline Canal Source segment is little travelled -- perhaps because it doesn't connect to the rest. From Waterton Rd outside Waterton Canyon, the trail follows the canal through a rural setting. At the downstream end, before reaching the trail end at Plum Creek, you can connect to the trails inside Chatfield State Park.
A complete description is available in Jefferson County South Urban Trails.
The Sand Creek Trail will soon complete a connection from the Platte River Trail to the Highline Canal path north of Denver. The majority has is already open, running on concrete and soft-surface, by new parks and lakes. You may share the trail with horses!
A complete description is available in Denver North & Aurora Urban Trails and Take A Bike!
Head south on I-25 to the Air Force Academy, and catch the Monument Creek Trail. This soft-surfaced trail runs from Palmer Lake through the Academy grounds, and the stretch inside AFA is perhaps the nicest, with trees and scenic creek views. Once the trail hits Colorado Springs, it becomes paved, running beyond downtown.
A complete description is available in Southern Colorado Urban Trails.