There's something about an empty prison that's just downright scary.

When I walked through the iron gates of Eastern State Penitentiary in Philadelphia recently, I regretted not bringing a friend. With its stone walls and guard towers, this former prison looks like a castle. But inside, it's clearly not fit for royalty. Long hallways are lined with cells, each one with peeling paint, a rusted bed frame and a toilet. The temperature outside was above 70 degrees, but inside it was 10 to 15 degrees cooler. I shivered, and not just from the cold.

I'd come to see what AOL City Guide last year called the No. 1 haunted house in America. Each year, from mid-September to early November, this historic landmark in the city's Fairmount neighborhood becomes the site of "Terror Behind the Walls," an elaborate nighttime theatrical production involving strobe lights, digital sound effects and 150 actors dressed as prison guards and prisoners.

Built in 1829, Eastern State was one of America's first penitentiaries. The goal of the Pennsylvania system was unique: to reform the prisoners and move them toward real penitence, rather than simply punish them. The inmates served their time in solitary confinement, allowed outdoors into a private yard for only 30 minutes each day. Whenever they were outside their cells, they wore hoods to prevent distraction, in the hope that they would reflect on their crimes and repent. After visiting Eastern State, Charles Dickens condemned the solitary confinement as "cruel and wrong."

In 1913, the state abandoned the practice, partly because there wasn't enough space to give each prisoner his or her own cell. Intended for 256 inmates, the prison held 1,700 by the 1920s. Notable residents included Al Capone.

The prison was closed in 1971 and opened for tours in 1994. The city, which owns the property, has stabilized the building but won't do full restorations so as to keep it authentic. Hence the peeling paint, the leaks and the musty smell. I wondered why tourists would visit a prison in the City of Brotherly Love, even one that Kelley proudly described as "the Alcatraz of the East Coast." But apparently people like prisons: Last year, the penitentiary drew 209,380 visitors.

We arrived around 7 p.m. Once inside, we spent most of our time in the dark. We walked in line through chain-link fences, under guard towers. Amid fog and loud bangs, actors with fake blood smeared on their faces popped out at us every few minutes.

After a few minutes, we made it to the infirmary, where actors dressed as doctors performed fake procedures in the empty operating rooms and the morgue.

It was all fun and games, really, until we got to the walk-through sterilization chamber, where the visual effects made it seem as though the room was spinning around us. I got so dizzy I had to stop.

In another room, we donned 3-D glasses, which made skeletons and other ghoulish figures pop out of the walls. Near the end, we entered the "Night Watch" portion of the tour, where we were left to feel our way out of the back hallways of the penitentiary in the dark. The strobe lights were disorienting me. Then, thankfully, we were out.