The only legal spot to skateboard outdoors in Philadelphia is at the setup in Roosevelt Park. It’s at the far end of the park, tucked under the highway overpass. It’s a good space, large, very popular with skateboarders. You can see some skilled people here. (Some get a bit impatient with slow young novices, mainly because they’re afraid they’ll run them over. Bring a helmet and kneepads.) Roosevelt Park, Broad and Pattison Sts. Opposite the First Union Complex. Open dawn to dusk daily.
Skateboarding outdoors anywhere else in Philadelphia is illegal and carries a $300 fine. Love Park has been renovated, specifically to block skateboarding.