The Eastern State Penitentiary is located in Philadelphia PA. The Penitentiary, built in the 1820’s-30’s, is a National Historic Landmark now open to the public and is run by a non profit group who offer guided and unguided tours of the old prison. It is a unique place and I highly recommend a visit if you are in the Philadelphia area.
(For the follower who asked for a post on it! Such a beautiful site!)