There are two versions of the Inca Trail to Machu Picchu: the long one and the short one. We did the short one, which goes about 9 miles, rises 1500 feet, and took me about 9 hours. This website has a good description.
(click to enlarge) Start by hopping off the train, crossing the bridge, and registering at the checkpoint. (The number of hikers per day is limited.)
(click to enlarge) There are many Inca ruins in the Sacred Valley. Chachabamba, just after the checkpoint, is relatively small but very attractively situated.