The Cascadilla Gorge Trail is the most useful walk in Ithaca. It begins on the eastern edge of the Commons and climbs three-quarters of a mile up alongside a chain of eight waterfalls, ending at the base of College Avenue on the Cornell campus. The trail uses cut stone steps in places — when it's open, no other approach to the campus from downtown is half as beautiful.
The trail closes through winter when ice on the rock makes it dangerous; check the Cornell Botanic Gardens website for current status. In spring and autumn it's transcendent. Half an hour up, then either take the TCAT bus back down or carry on into Collegetown.