I don't think there's anything permanent set up in Philly. There's plenty of places you could ride a cross bike, Valley Green on the west side of the park would be good, Penny Pack has some trails that you could ride a cross bike on as well. I usually just try and find a school or park near the house and set a course up. Depending on where in Philly you are that might be easier said than done, good luck.
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