Once confined to the backyard of that eccentric dude down the street with the garden shed filled with homemade props, haunted "walk-through" attractions have emerged from somewhat hokey beginnings to become a bustling multimillion dollar industry. Each October, thousands of commercial "haunts" pop up across the country for brief but lucrative seasons.

PHOTOS TO SCARE: 10 places to visit in the spooky season

Boasting story-driven plots, high-end special effects and professional costumes and makeup that give "The Walking Dead" a run — or should we say a lurch? — for its money, haunts evolve each year to keep petrified patrons coming back for more. And with each passing year, simulated haunted houses and farms become scarier, larger, more intense, more extreme. Gone are the days when hired werewolves and zombies and axe-wielding maniacs got close … but never touched. Now, a growing number of haunts offer more immersive experiences where physical contact is par for the terrifying course.

Manhandling aside, location remains key in the overall fright factor. After all, there's nothing quite as dread-inducing as attending a haunted house located inside a building that's rumored to be really haunted. Sure, vacant retail spaces in suburban strip malls are petrifying in their own special way, but you can't beat a haunt housed within, let's say, an abandoned prison, a derelict cement factory, a paranormally active cruise boat or the dank basement of a 100-year-old Elks lodge.

With an eye toward adaptive reuse, historical significance and overall bone-chilling uniqueness, we've rounded up 11 exceptionally eerie haunted attractions across the U.S. While these haunts might not be the biggest, baddest or goriest in all the land, they do offer uniquely atmospheric experiences that can elicit serious shivers even before you pass through the front doors.

1. The 17th Door in Tustin, California

We start our list with an exceptionally harrowing pop-up spook-house located in what may seem like a rather unexceptional locale. For many, however, nothing can curdle the blood quite like a suburban Southern California shopping center. And The 17th Door, an Orange County "haunted experience" that requires both a safe word ("mercy," in case you're wondering) and a signed waiver, is smack dab in the middle of one, flanked by Party City and Pier 1 Imports. Scary! Beware the ghost of previous tenant, Easylife Furniture!

But what The 17th Door lacks in exterior heebie-jeebies or haunted historical cred, it certainly makes up for in gruesomeness. Promising "30 minutes of escalating terror" with a special emphasis on "extreme thematic materials" and terrifying pig-demons, it's arguably 2015's most talked-about haunted attraction. "There’s a lot going on, where it’s very interactive and immersive and kind of invades your space," co-creator Heather Luther tells ABC 7. "You will get touched and you might get wet." Yikes. Good thing there's a Ross Dress For Less located right across the way.

2. Dark Harbor in Long Beach, California

A performer in the Dark Harbor haunted maze interacts with a prop horseA performer in the Dark Harbor haunted maze interacts with a prop horse. (Photo: Matthew Nelson/flickr)

Apparently, all it takes to revive a financially struggling luxury liner is to populate it with a "Thriller"-worthy troupe of fearsome fiends on a mission to scare the holy bejeebers out of all of those who embark. Just ask the Queen Mary.

The octogenarian cruise boat, permanently moored in Long Beach, California, as a hotel and historic tourist attraction since 1971, has experienced ups and downs over the years — mostly downs. Launched in 2010, Dark Harbor is a "unique haunted experience" featuring six monster-lined mazes "so daunting you'll sell your soul for the chance to survive," that has managed to lift the Queen Mary out of the red — while splattering a whole lot of red all over it. As reported by the Los Angeles Times, revenue from events held at the historic Cunnard Line vessel has jumped 400 percent over the past five years. As for Dark Harbor, annual visitor numbers continue to grow. Event organizers acknowledge that the Queen Mary's struggles as a hotel may have something to do with her reputation for paranormal goings-on, the very thing that's made the retired ocean liner such a Halloween hit: "The intrigue with the Queen Mary is that it's considered one of the most haunted locations in the world," says Charity Hill, director of entertainment for Dark Harbor.

3. The Dent Schoolhouse in Cincinnati, Ohio

The Dent SchoolhouseThe Dent Schoolhouse was allegedly the site of a grisly child murderer. Now it's a grisly haunted attraction. (Photo: The Dent Schoolhouse/Facebook)

Built in 1894, the Dent Schoolhouse is blessed with a truly horrific backstory. According to local lore in the northwestern outskirts of Cincinnati, from 1942 to 1955, a total of 20 children, all students at the school, disappeared without a trace. Around the same time, the basement of the red brick structure started to take on a pungent odor — a stench that the janitor, Charlie McFree, blamed on backed-up pipes. In a Krueger-esque twist, a group of vigilante parents, suspecting Charlie was up to no good, stormed the basement following another spate of disappearances. Here, they discovered the decomposing remains of the missing children, stuffed into the walls. The school was shuttered and Charlie McFree was never seen or heard from again.

Go figure that a small army of dead schoolchildren haunt the Dent Schoolhouse and Charlie McFree, good lookin’ guy that he is, is lurking around, too. While the veracity of the above yarn is obviously highly debatable, many area residents, the building's current owner included, do believe the long-abandoned public school is haunted by something. As for the grisly, high-octane annual haunted attraction spread out across the old classrooms — and the notorious basement — it's frequently named one of the scariest in the country. Whatever you do, try not to get sent to detention, okay?

4. Fear Factory in Salt Lake City

Old, abandoned warehouses and industrial buildings serve as the perfect blank slates for commercial haunts — they're creepy, rundown, usually located in dead-at-night parts of town and, most importantly, offer abundant raw space in which to create a nightmare from the ground up. Kansas City's historic West Bottoms district for example, features multiple haunted attractions amongst the antique emporiums and loft event spaces.

Rarely, however, do these ambitious adaptive reuse projects involve real supernatural activity. The Fear Factory is a notable exception — they don’t call it "Salt Lake City's only haunted haunted attraction" for nothing. Situated in the old Portland Cement Works, a long-shuttered late 19th century factory with a history of unfortunate workplace accidents (many involving the word "mangled"), this popular Halloween attraction also boasts one hell of a street address: 666 W. 800 South. As the even organizers put it, the building was "truly abandoned for a reason." In addition to Fear Factory's gore-drenched "experience", the old Portland Cement Works is open for organized paranormal investigations and has been featured on the Travel Channel's "Ghost Adventures."

5. Haunted Prison Experience in Mansfield, Ohio

A ghostly look inside the Ohio State ReformatoryA ghostly look inside the Ohio State Reformatory. (Photo: Tom Hart/flickr)

Completed in 1910, Ohio State Reformatory is best known for appearing in a non-horrific film adaptation of a novella written by an author famous for horrific film adaptations, if that makes sense. This is Shawshank State Penitentiary.

Built in a trio of architectural styles (Queen Anne, Gothic and Romanesque Revival) as a means of inspiring inmates to "turn away from their sinful lifestyle, and toward repentance," the castle-like structure, added to the National Register of Historic Places in 1983 and completely decommissioned in 1990, attracts a decent amount of Stephen King-related tourism as a stop on the so-called Shawshank Trail. The reformatory is also (allegedly) haunted as all get out — in addition to the architecture and King associations, some of the main draws are the organized ghost walks and private ghost hunts. And of course the Ohio State Reformatory is also home to an annual haunted experience. Produced by Haunted X, the Haunted Prison Experience switches things up every year (this year, it's a witchcraft theme) to keep the scares fresh. The award-winning haunt also takes its age restrictions very seriously: no kiddos under 13 are permitted, even with an adult escort, and birth certificates or report cards must be furnished by driver license-less patrons to prove their age.

6. Horseman's Hollow in Sleepy Hollow, New York

Those who prefer their haunted attractions to resemble nightmarish living history museums (think: blood-stained periwigs and period murder implements) should gallop, tout suite, to Horseman's Hollow. Produced by preservation-minded educational nonprofit Historic Hudson Valley, Horseman's Hollow is one of several popular events occurring in and around Sleepy Hollow during the Halloween season including the epic Jack O' Lantern Blaze. However, it's the only one "not suitable for adults who are claustrophobic, have heart or respiratory conditions, are prone to seizures or have other chronic health conditions."

Envisioning a "town driven mad" by a certain beheaded Hessian, Horseman's Hollow is held on the grounds of Philipsburg Manor, a real-deal 18th century Dutch farmstead complete with gristmill, manor house and barn. A perfectly lovely place to take a walk with your granny during the daytime, the manor is even mentioned in Washington Irving's short story that put the quaint village of Sleepy Hollow on the map. And while not the scariest haunt on this list, Horseman's Hollow is tremendously atmospheric and does a decent job of staying (mostly) historically accurate right down to the Revolutionary War zombie soldiers and complete absence of bloodied power tools.

7. Nightmare on the Bayou in Houston

Billed as "Houston's only haunted house with real ghosts," Nightmare on the Bayou prides itself on its unnerving location directly next to Olivewood Cemetery. And go figure that paranormal researchers recognize historic Olivewood — established in 1877, the immense and once-overgrown cemetery is the final resting place for freed slaves and many of Houston's early African-American residents — for its high frequency of eerie and inexplicable activity. Ask anyone in Houston Heights if they know of a legit haunted cemetery, and they'll point you in the direction of Olivewood.

While this sprawling — this is Texas, after all — indoor/outdoor haunt isn't held in Olivewood itself (because that would be just wrong), some of its restless spirits have apparently migrated past the cemetery gates and onto the adjacent property where they join a cast of ghouls, goblins, menacing clowns and redneck zombies sporting seriously alarming flesh wounds. And wouldn't you know it, Nightmare on the Bayou's other neighbor is a party and costume supply store, which, rumor has it, is also home to a few resident specters, including one that store owner Bob Wright has affectionately named "George." (The self-described practical joker also operates Nightmare on the Bayou.)

8. Pennhurst Asylum in Spring City, Pennsylvania

A ruined building on Pennhurst Asylum campusThe ruins of Pennhurst Asylum attract ghost hunters and those looking to get scared out of their wits. (Photo: Thomas/flickr)

In 1987, the notorious Pennhurst State School and Hospital, a facility originally known as the Eastern Pennsylvania State Institution for the Feeble-Minded and Epileptic, was closed following decades of overcrowding and allegations of patient abuse. While a small section of the sprawling campus has since been redeveloped, other buildings remain abandoned and in ruins — popular spots, obviously, with ghost hunters and urban explorers. And then there's the administration building. An imposing brick structure with distinctive portico and cupola, the old administration building has also been spared from further decay and repurposed — into a truly unsettling hospital-themed haunted attraction.

While an adaptive reuse project that transforms a stigmatized property with a painful past into a moneymaking Halloween attraction might be deemed as insensitive, it hasn't stopped thrill-seekers from flocking by the busload to Pennhurst Asylum, now in its fifth season. "A lot of people believe ... the spirits of people [who] have suffered and died in this institution are still in here. A lot of people feel that way. I mean, that definitely adds to the thrill of it," one visitor told NPR in 2010. Organizers have incorporated numerous artifacts salvaged from the state school into the attraction; even a section of the network of underground tunnels running beneath the hospital grounds have been reopened. As for the gore-splattered actors that bring Pennhurst Asylum to life each night, owner Richard Chakejian admits that some have broken character and walked off the job following eerie encounters. "The fear is real at Pennhurst. This is a haunted place."

9. Ruby Falls Haunted Cavern in Chattanooga, Tennessee

A cave-dwelling monster poses in the parking lot of Ruby FallsA cave-dwelling monster poses in the parking lot of Ruby Falls. (Photo: Ruby Falls Haunted Cavern/Facebook)

Those suffering from claustrophobia or who found themselves traumatized by 2005's girls-only-spelunking expedition-gone-bad film "The Descent" may want to take a pass on Eastern Tennessee's most distinctive seasonal horror show, which isn't located in a house (or a facsimile of a house) but in an honest-to-goodness cavern — a cavern that just happens to be located 26 stories underground and "crawling with monsters."

Located in the same subterranean complex as Chattanooga's famed underground waterfall Ruby Falls, the story-driven Haunted Cavern boasts an elaborate mythology populated by a gruesome cast of deranged mutants in need of some serious dental work. Just the act of descending beneath Lookout Mountain in an elevator — excuse, "hellevator" — as terrified screams rise from the depths below is pulse-raising enough. To be clear, not all of the Haunted Cavern takes place in a cave that's not normally open to tourists — the second portion of the haunt is located aboveground. Still, closed-toe, slip-resistant shoes and clothing you don't mind getting "a little dirty or wet" are highly advised.

10. Scarehouse in Etna, Pennsylvania

No doubt about it, the most bloodcurdling basement in all of suburban Pittsburgh is at the old Elks Lodge No. 932, a 100-year-old building across the Allegheny River in Etna. At the very least, it's certainly the only basement in suburban Pittsburgh where you'll encounter "high voltage effects, exposure to electricity, sexual content, very low lighting, tight spaces, strong scents, profanity, moments of complete darkness, water, physical contact, violent situations and high impact scares."

One of several elaborately produced haunts at the lauded ScareHouse, The Basement is an immersive "fear experience" with separate admission and a laundry list of caveats. Brave souls over the age of 18 must sign a waiver before descending into the lower levels of the historic Elks building, which, by the way, is also believed to be haunted. It's that intense. While in The Basement, there will be no touching (the actors will, however, touch, restrain and blindfold you). And refunds are not provided, even if you call out the safe word "Bunny" at any point. "The Basement is based on what research tells us humans' biggest fears are today," Margee Kerr, the fear-specializing sociologist who helped to cook up the concept, explained to Pittsburgh CityPaper. "It very much is meant to tap into deeper issues that are uncomfortable and unusual."

11. Terror Behind the Walls in Philadelphia

Nurses pose in the Terror Behind the Walls haunted attractionNurses pose in the Terror Behind the Walls haunted attraction at the Eastern State Penitentiary. (Photo: J.R. Blackwell/Eastern State Penitentiary)

The lure of Terror Behind the Walls is simple, straight-to-the-point and incredibly nightmarish: "a massive haunted house in a real prison." And, oh yeah, the prison, Philadelphia's Eastern State Penitentiary — the hulking gothic fortresses opened in 1829 as the world's first true penitentiary with an emphasis on solitary penitence in lieu of group punishment — is also totally haunted. What else would you expect from a creepy, castle-like structure that was in the business of imprisonment for nearly 150 years? And, yes, the massive gargoyles flanking the penitentiary's front façade are a new-ish addition, although it looks like they could have easily been there all along.

Held within the cold, unforgiving stone walls of ESP, the defunct prison-turned-museum's annual haunt is frequently named one of the country's scariest — and rightfully so. The nonprofit behind the long-running fright-fundraiser — the same organization that leads decidedly less horrific daytime tours of the imposing historic landmark — really pull out all the stops without simply relying on the penitentiary's inherently unsettling (think: Scooby-Doo meets Alcatraz) atmosphere. Featuring six uniquely ghastly experiences spread out across the six-acre complex's radial floor plan, Terror Behind the Walls cranks the unease up a notch by allowing patrons to opt for a more interactive experience — that is, an experience in which they're touched, grabbed and pulled from their groups and thrown into solitary confinement by demonic prison guards. New for 2015 is "Inside Quarantine: 4-D," a delightful-sounding diversion in which you're "immersed in the experience of being exposed to an infectious outbreak — with symptoms like hallucinations, distorted depth perception and other mind-altering effects."

Matt Hickman ( @mattyhick ) writes about design, architecture and the intersection between the natural world and the built environment.

11 exceptionally eerie haunted attractions
We've rounded up 11 exceptionally eerie haunted attractions across the country sure to tingle your spine.