Near Ithaca, the Shindagin Hollow State Forest has 6 miles of trails open to hiking.
To reach mountain biking at the trailhead, take SR79 past Brooktondale. Turn right on West Creek Road and go into Caroline. Turn left on South Road, which comes in at a funny oblique angle. The Shindagin entrance we use is at Gulf Creek road (right turn off of South); it goes by a farm and then connects with some old logging roads in the forest.
Overall, Shindagin Hollow State Forest is the 21st most popular mountain bike trail of all 48 mountain biking rides in New York.