PHILADELPHIA -- Entering the rusted iron gate of Eastern State Penitentiary, with its 30-foot-high stone walls and long-abandoned guard towers, is eerie enough in the light of day. But the former Philadelphia prison, now a national historic landmark and tourist attraction, has an even creepier presence when night falls.

During the Halloween season, this massive relic of a bygone penal system becomes "Terror Behind the Walls," a haunted house that each weekend attracts hundreds of visitors to its Spring Garden neighborhood at 22nd Street and Fairmount Avenue. Funds raised during the mid-September to Nov. 1 haunted house season are used for Eastern State's continuing preservation.

Last year, more than 209,000 visitors toured the prison, which offers daytime tours and special guided tours through November.

"It's a building that was designed to intimidate, to deter crime simply by its gruesome appearance from the outside," said program director Sean Kelley. "It's a big old castle built to dominate the landscape and strike fear in anyone who sees it."

On a mild fall evening in October, the atmosphere outside the gates of Eastern State is more like a Halloween party, with prison "guards" dressed in uniforms and ghostly makeup, ghouls walking about on stilts and vendors selling hot dogs, necklaces and fake eyeglasses that light up.

Some fright-seekers step off the "ghost bus," a trolley that travels between the prison and parking lot ($10) at the Philadelphia Zoo several blocks away. During the ride, a guide shares ghost stories.

In front of the prison, tour-goers joke and laugh as they fill out yellow waiver forms before heading inside the gate. There, visitors get their photo taken with a zombie on stilts. A package of five pictures will set you back $20.

Ranked in 2008 as the No. 1 haunted house in America by AOL City Guide, Terror Behind the Walls is more of a good old-fashioned scare than anything truly terrorizing. Crazed guards and zombie-like inmates pop out from everywhere as visitors make their way through a maze of dark corridors.

Each segment of the haunted house has its own staff, lighting effects and sound tracks. One part of the tour requires 3-D glasses, which make the skeletons and gargoyle-like figures seem to pop out from the walls. Another segment called Night Watch requires visitors to use a tiny flashlight to cut through the pitch-black darkness. New this year is a segment called Infirmary, where "doctors" can be seen pulling out the organs of their inanimate patients and asking for live volunteers to take their place.

"We do our best to make it a terrifying experience," Mr. Kelley says.

The lightheartedness and joviality of a haunted house is an unlikely scenario for a prison touted as the world's "first true penitentiary, a prison designed to inspire penitence or true regret in the heart of prisoners."

Opened in 1829 with 250 cells, Eastern State was built like a giant wheel with a hub and seven cell blocks radiating from it. The prison had indoor plumbing and central heat before the White House did. Each prisoner had his own cell with a skylight and exercise yard, the thought being that solitary confinement with labor leads to repentance. This was called "The Pennsylvania System" and served as a model for about 320 other prisons throughout the world.

During rare times that prisoners were in common areas, their faces were covered with hoods to limit their contact with each other and with guards. Eventually, eight more cellblocks were added, bringing the total number of cells to 980.

Eastern State attracted visitors even then. Charles Dickens, who toured the prison in 1842, later wrote: "The system is rigid, strict and hopeless. Solitary confinement, I believe, in its effects, to be cruel and wrong."

The years following Dickens' visit saw the eventual breakdown of the solitary confinement system, but it would be another 71 years before it was officially abandoned in 1913.

Throughout its 142 years as an active prison, Eastern State housed a number of noted inmates including the infamous Al Capone, bank robber "Slick" Willie Sutton and "Pep the Dog." Legend has it that Pep was sentenced to prison in 1924 by Gov. Gifford Pinchot for killing his wife's cat. Newspaper accounts, however, indicate that the governor donated his own dog to boost inmate morale. Either way, Pep received a prison number and a mug shot.

While the other prisoners made due with stark walls, Capone's cell was decorated with paintings, a cozy wing chair, lamps, a highly polished writing desk and a cabinet radio. His release in 1930, after an eight-month sentence, drew a huge crowd outside the prison gate, hoping for glimpse of the celebrity gangster.

Eastern State closed as a prison in 1971 and opened as a historic site in 1994. Now, tourists gather outside a replica of Capone's cell to snap photos. Other stops along a 40-minute audio tour, narrated by actor Steve Buschemi and included in the admission price ($12 for adults, $10 for seniors and $8 for students and children), are Escape Attempts, The Hole and Notable Inmates. Visitors can also wander at their leisure through the ancient cellblocks with their peeling paint and crumbling plaster. One cell has been restored to look the way it did in the days when inmates instead of tourists roamed the grounds.

Doug Oster writes a blog, "Growing With Doug," exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.