Some background about the cave:
The cave still stands (if a cave stands?) because it's a historic site of sorts. It was the headquarters of the Kelpius Community, who were a group of German mystics who lived in the area in the 1600s and were sort of a doomsday cult.
I don't know how big the cave appears from that photo but it's not all that big. It goes maybe eight feet back from there. However, it's REALLY dark in there, even in daylight. There's some Satanic spraypaint in there, along with usually discarded empties. I've seen one or two degenerates smoking weed in there a few times, too. I've never been in the woods near the cave that late and was pretty worried about what I might find. I thought there might be a teenage beer bash which I wouldn't be scared of. But every so often police helicopters will fly over my neighborhood and have a spotlight over the park because I assume some criminal is hiding out.
It's in Wissahickon Park. Wissahickon Park extends through all of northwest Philly (East Falls, Roxborough, Manayunk, Andorra, Chestnut Hill, Mr. Airy and Germantown) which is a gigantic expanse of land. It's bigger than Central Park by a significant margin. The Wissahickon Creek goes through the middle of it with all sorts of hiking trails that wind their way through the park. It's AWESOME. I've seen cranes and red-tailed hawks and deer within a few feet of me. My friend saw a bald eagle once. People fish in the creek. There's also a swimming hole, an Indian burial ground and a recreated old mill town.
I live right by one of the trail openings which winds past this cave. Access to the park is one of the primary reasons why I live in this section of the city.