Mountain biking is still in its infancy in Peru, although fat-tire options are growing fast. Colca Valley and Canyon, Huaraz and the Callejón de Huaylas, and the Sacred Valley are the major areas for off-road cycling. The Manu jungle is also good for hard-core biking. Several tour companies in those places rent bikes, and the quality of the equipment is continually being upgraded. If you plan to do a lot of biking and are very attached to your rig, bring your own.
My favorite mountain-biking spots are horse and mountain trails in the spectacular Callejón de Huaylas, which provide the kind of amazing climbing found in the Rockies of the western United States and mountain views that are second to none. Mountain bikers, along with other adventure-sports fans, descend on Huaraz and the valley every June for its celebrated Semana del Andinismo. The Colca Valley is also an outstanding region for hard-core mountain biking, though there are fewer tour outfitters targeting the area. For gentler but also incredibly scenic trail riding, you can't beat the Sacred Valley.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.