Located right in town, Ithaca Falls towers at 175 feet high, and it's nearly as wide.  The falls is visible from Lake Street, but you can walk down a short path to the base of the falls (dotted purple line on the map below).  There's also a very nice overlook from Willard Way (green star on the map below), with a prayer/meditation house just behind it.  Above the falls is a dramatic section of gorge, the bottom of which can be accessed from very steep paths descending from the trail (dotted green line below) that runs between Stewart Avenue and the suspension bridge (solid green line below).

Links for Ithaca Falls and Fall Creek Gorge:
http://gowaterfalling.com/waterfalls/ithaca.shtml
http://www.plantations.cornell.edu/collections/natareas/Public/FCGorge/FCGorge.htm
http://www.naturalhighs.net/waterfalls/falls02/ithacafalls.htm
http://images.beggerlybend.com/photos/gorges/fc/index.html
http://www.angelfire.com/ny4/waterfalls/fallcreekgorge.html