Unreal horrors at Terror Behind the Walls

I recently encountered evil surgeons hacking at body parts, raving demons, bald bloody creatures swinging chainsaws and cinderblocks, devil nurses and tentacled shaggy demons.

But it wasn’t some drugged-up fever dream. It was at Terror Behind the Walls (TBTW) at Eastern State Penitentiary in Fairmount.

The TBTW experience starts on the sidewalks outside, where performers in prison guard uniforms strut up and down staring at passersby, making creepy statements to them — whether they are ticket buyers or not.

Inside the stone prison, all visitors sign a legal waiver (unnervingly labeled as an “execution form”) before the haunting can truly begin.

They also have the option of selecting the “interactive” experience, offered since 2013 — meaning the monsters can touch you, take you out of your group and even kidnap you for an especially horrifying experience.

On a recent visit, I didn’t expect this haunted house to surpass an adult fear threshold, honed on years of horror films and roller coasters.

But TBTW is uniquely frightening, due to the incredible performances of the small army of more than 200 actors and performers with brilliant makeup and costumes that populate the prison.

Soon after I entered the haunted house, the thrills started coming hard and fast. Within minutes I realized that behind every corner, wherever you are not looking, a new monster will be swooping down screaming gibberish or threats at you, an air machine may emit staccato gun-like bursts of air at your body, or someone will be reaching out of a wall to grab you.

You start to sweat, your heart begins to race, and suddenly you’re in fight or flight mode.

TBTW is divided up into six sections, each with its own particular design theme and type of monsters. Visitors follow the maze-like path in a line. But it’s hard not to run at times.

I took the “interactive” trip and thus had the experience of being grappled by a demonic dentist who flung me into a chair and threatened to destroy my teeth with a buzzing device.

One ghoul dove at me near ground-level cutting at my leg with a fake chainsaw that roared like a real one.

I was also forced to go down a slide to a bizarre furnace room where zombies crushed my hand. Later I was dragged into an elevator where a monster shouted at me, “You’re going to have to work in the mines! You’re going to be one of us!”

But the worst of all was just when I thought things had ended, but instead, I was dragged off by zombie riot police, blindfolded and thrown into a prison cell.

The haunting becomes quiet scary when there are more monsters than regular people around you, and given the history of Eastern State, being placed in solitary confinement in a prison cell and ordered to “confess” by a group of monsters was genuinely terrifying.

But after I “confessed” to stealing 3-D glasses from earlier in the tour, I was re-blindfolded and walked to a hole in the wall that I was allowed to crawl through to escape.

Prison turned haunted house

Eastern State Penitentiary on Fairmount Avenue was built in 1827 and closed in 1971.

It is recorded as the first U.S. prison to use solitary confinement. Famous prisoners include Chicago gangster Al Capone, who spent eights months there.

Since the 90s, it has been adopted for use as a haunted house, and also opened as a museum.