Join a local Jeep club, like BMJA. Your best bet is going to be to find some private land you can wheel. I know of a couple, but I can't give out the info for self preservation sake. But they do exist. But you are going to have to know someone to find it.I live about 1/4 mile from the Chester County Hospital.
Pine Barrens are awesome, but i would not recommend going there alone. Thats actually the place where i broke my Jeep. And the place is about 40 minutes from Philly.Look over at jeeperz.com under PA, its a local club that is really active. The pine barrens are supposed to be decent and there is always the philly arport, yes the philly airport. Hit me up, im always ready to wheel or work on the jeep