This forest is located partly within Tompkins County.  To get here, take NY Route 79 east from Ithaca, and just after you enter Tioga County, turn left on Robinson Hollow Rd.  Beam Rd splits left from Robinson Hollow, and both continue through state land.  There are some nice trails to be found here, and I haven't followed all of them, but a few are shown below.

Shown in dark blue are a series of trails west of Beam Rd.  Just south of the triangle-shaped pond (but past the snowplow turnaround), a trail heads east from the road.  A spur I haven't taken heads south, while the main trail splits near the ridgeline.  One branch goes north, then turns east (downhill), then reaches a private pond.  The other branch heads south along the eastern edge of the ridge.  After a while, this trail forks and I chose to head west (uphill).  After wandering over the relatively flat ridgetop, this trail plunges down a steep hillside to meet up with Beam Rd.

A section of the Finger Lakes Trail passes through the western part of Robinson Hollow State Forest (labelled in orange below).  It's about four miles, so we chose to do a one-way trip, leaving one car on Harford Rd (at the north end) and one on Route 79 (at the south end).  From Harford Rd, the trail is a little hard to spot, but it's not far east from where the road crosses into Town of Dryden.  Initially, the trail heads uphill, crossing an old roadbed a couple of times.  As you walk along the high ground through pleasant forest, the trail crosses a dirt road, another trail, and a pipeline (none of which have I followed).  After heading straight south along the western border of the forest, the trail drops into a creek valley.  The creek is followed for a time and then crossed, but at this crossing, note the blue-marked side trail that leads to a lean-to.  Next, the main trail climbs briefly, then heads south along the hillside, eventually merging with a dirt road (lavendar below).  The trail departs from this road a short while later, but I don't recommend taking it.  Judging by the fresh "No Tresspassing" signs, it appears the landowner along Route 79 is no longer welcoming hikers.  Instead, you should be able to follow the dirt road back down to Robinson Hollow Rd.  To find the dirt road from Robinson Hollow Rd, go north from Route 79 and look for the trail just after the small bridge (across from a house whose driveway is labelled "Rock Bottom Road").

Edited, map from http://www.topozone.com