A walk through Eastern State Penitentiary offers a glimpse into a world rarely seen by ordinary citizens. It forces one to imagine the lives of those behind bars and to examine the controversial history and ideals of the criminal justice system—past and present.

When it opened in 1829, the penitentiary’s novel design and philosophy were considered radical experiments. Benjamin Franklin and Benjamin Rush, who were members of the first prison reform group in history—the Philadelphia Society for Alleviating the Miseries of Public Prisons—supported the prison. Famed architect John Havilland won the design competition and one of his competitors, William Strickland, oversaw construction.

An alternative to the overcrowded prisons of the time, the Quaker-inspired goal of Eastern State Penitentiary was to reform criminals through strict isolation. It was founded on the belief that when left to their own devices without the influence of the outside world, prisoners would become “penitent,” or remorseful. Both the concept and architecture soon became a model for prison design worldwide.

Approximately 300 prisons on four continents were modeled on the innovative floor plan, in which a central guard post is flanked with multiple sections extending from the center.

The castle-like structure occupies 11 acres in what was then considered the outskirts of town, today’s Fairmount neighborhood. It was the most expensive structure ever built at the time. Prisoners ate, worked, and lived in their cells, with an hour each day outdoors in a small private courtyard. When it was necessary to move through the public spaces, hoods were placed over their heads so they couldn’t even see one another.

While the intentions of the founders were presumably good, the failings of the isolation system quickly became clear and the prison faced accusations of inhumane treatment. The first investigation into the possibility of questionable practices took place in 1832; in 1842 Charles Dickens visited and said: “The system is rigid, strict and hopeless solitary confinement, and I believe it, in its effects, to be cruel and wrong.” It wasn’t until 1913 that the confinement system was abandoned.

Among the famous prisoners who did time here was Al Capone, who was apparently given royal treatment during his eight-month stay. A peek into his restored cell reveals a cushy apartment with antiques, rugs, oil paintings, and the sounds of a waltz that frequently played on his radio.

In 1970, the prison closed, and there was talk of tearing it down and using the space for commercial property. Fortunately, a task force set out to preserve what is now considered a National Historic Landmark. In 1994, Eastern State Penitentiary opened for daily tours. Visitors are required to sign a waiver stating that they are aware of the poor condition of the building before entering, but the areas deemed unsafe are closed to the public.

Different tours take place throughout the day in which guides tell stories of prisoners, escapes, and more, but the well-made self-guided audio tour, “Voices of Eastern State,” is the best way to get the full picture. Actor Steve Buscemi’s voice, along with those of real prisoners and guards, guides you to more than 20 fascinating sites throughout the prison that reveal its rich history.

If you happen to be in town and have a high tolerance for fear, the already-spooky site is transformed into the annual Terror Behind the Walls, a haunted house, every night in October.