The Tarsier room is at the back of O'Reilly's Sebastopol buildings.
The address for the entire complex is 1005 Gravenstein Hwy. North. If you're coming from downtown Sebastopol, just head north on 116, go past Pacific Market and Longs, and then it's a few hundred yards ahead on your right.
Turn right into the main, driveway near the center of the complex. There's a walkway between two buildings straight ahead, which is where you will be walking. But first, turn right and park your car.
Walk between the two large buildings, and then turn right on the walkway that runs behind the main building. The Tarsier room is immediately on your left (it is separate from the main building).
Trivia note: check out the lawn behind the buildings in the aerial photo on the left. The photo was apparently taken during Foo Camp.