It starts out on Forbidden drive which is fairly heavily traveled. However, after passing the Valley Green Inn (and before it), there are numorous turn-offs that can be made. Most of them start out with a steep climb then level out or climb some more and then...the downhill. Some really tough singletrack lies ahead after the climb.
How to get there:
From Center City Philadelphia, head down the East River Drive and then go up Ridge Avenue. Follow Ridge Ave until you hit Roxborough Ave. Make a right on Roxborough and get on Henry Ave. Follow Henry until you see a sign for Valley Green. Make a right and follow the forest road until you get to the parking lot.