The Colorado Trail celebrated its fortieth anniversary in 2014, and although it was designed for hiking, the trail's 28 segments are mostly mountain-bike-friendly, too (with the exception of six wilderness areas that you have to detour around). If you were so inclined, you could pedal out from Denver and end up in Durango some 535 miles later in a couple of weeks or so. Colorado Trail "completers" tend to throw around phrases like "life-changing," but even a day trip along any of the trail's segments is worth doing. Either way, get copies of the Colorado Trail Foundation's official guidebook and the CT map book at coloradotrail.org to plan it out properly.
Readers' choice: Lair o' the Bear