You're probably thinking of Alden Park apartments way down at the other end of School House Lane, off of Wissahickon Ave. If it was a retirement apartment building at one point it no longer is. I went to school at Philadelphia University and knew a few friends that lived there.

When I was let go from my job I did a lot of hiking in Fairmount. Mostly the Wissahickin trails, but the Belmont area trails are pretty dope too. John Heinz National Wildlife Refuge is really nice too. I also played disc golf regularly at Sedgley Woods. It was nice to get out of the house especially in the colder months, and the best part was they're all free, except for the gas to drive to each.