In Philadelphia, haunted houses aren’t just for kids. Each October, the city’s scariest structure — the slowly eroding ruin of a prison once known for the most oppressive incarceration tactics in the country — transforms into an interactive horror show.

Terror Behind the Walls at Eastern State Penitentiary regularly ranks among the world’s best adult Halloween installations. But this year’s edition is freakier and more adrenaline-pulsing than ever.

If you’ve been in the past, get ready to be impressed. This is the first year ESP didn’t host the Fairmount neighborhood’s late summer Bastille Day party, which organizers said lost the institution money every year — and it seems like that freed up time, funds and attention to make Terror even more intense.

Credit: Danya Henninger / Billy Penn

The freaky decor and lighting at the 11-acre historic site have been kicked up several notches. Each of the six segments in the attraction looks like the set of a major motion picture, and the whole thing is staffed by more than 200 professional actors.

How serious things are about to get becomes apparent when you get to the front of the line and have to sign a waiver form.

Credit: Danya Henninger / Billy Penn

Realistic animatronic models pop out of unexpected crevices in the arched stone cellblocks where real prisoners were once held in mind-numbing isolation. Shouts of “Boo!” from the live players make even more of an impact when you’re navigating dank corridors once patrolled by merciless guards.

Hallways strewn with rusty battle implements and shreds of tattered clothing lead you through twists and turns, and when the floor shifts below your feet thanks to a layer of slippery tiles piled atop one another, it’s truly unnerving.

Credit: Danya Henninger / Billy Penn

You’re already disoriented by the time you get to the section that’s supposed to be a quarantine zone and are handed 3-D glasses. Pop them on and the whole interior starts to swirl — including one part where you quite literally have to walk through a tunnel as the neon-striped walls spin 360 degrees around you.

If you opt in by putting on a “tracker” glow necklace, the ghosts and ghouls will make the experience even more interactive.

Example: you might end up participating in a satanic ritual, hoisting your hands above your head while chanting “Blood and bones! Blood and bones!” (It’s fun, swear.) Or being pulled into a dentist’s chair as a zombie nurse threatens to wrench your teeth out one by one.

Credit: Danya Henninger / Billy Penn

The attraction runs throughout the month of October, with pricing that starts at $24 per person during the middle of the week and tops out at $44 on some weekends. Folks under 18 have to must have a signed parental waiver to attend, and there are special Family Nights for kids aged 7 to 12. For those 21 and over, there’s a bar at the end of the route, called “Speakeasy at Al Capone’s” after the prison’s most famous inmate.

Scroll down for more pics from one of the trippiest legal experiences available in Philadelphia.

Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn
Credit: Danya Henninger / Billy Penn

Danya Henninger is director and editor of Billy Penn at WHYY, where she oversees the team, all editorial decisions, and all revenue generation — including the membership program. She is a former food...