Cascadilla Gorge is centrally located between downtown Ithaca at the bottom end, and Collegetown/Cornell at the top end (making a convenient 'scenic route' for walking up or down East Hill).  And yet, stepping into Cascadilla can make you feel like you're a long way from any town.  The high-walled gorge has a series of scenic waterfalls.  Continuing upstream from Collegetown, Cascadilla is more a valley than a gorge, but this stretch makes for a nice, short walk in the woods.

Links for Cascadilla Gorge:
http://www.plantations.cornell.edu/collections/natareas/Public/CasGorge/CasGorge.htm
http://gowaterfalling.com/waterfalls/cascadilla.shtml
http://images.beggerlybend.com/photos/gorges/cg/index.html
http://www.angelfire.com/ny4/waterfalls/cascadillagorge.html
http://www.ilovenyphotos.com/ithgorges/cascadilla1.html
http://www.ddt120.com/galleries/index.asp?GID=3
http://naturalhighs.net/waterfalls/falls02/caschoodoo.htm