WARNING: SPOILERS!

Pennywise terrorizes the entirety of Derry, Maine, but in the new adaptation of Stephen King’s horror novel It, the clown’s home base of operations is an abandoned old Victorian known as the Neibolt House. It’s here that the children known collectively as The Losers' Club discover the evil that lurks all around them and eventually confront the maniacal spirit clown in an intense showdown.

Faced with a relatively limited budget of $35 million, director Andy Muschietti decided that he would have to break the house up into several elements. He built the facade in an abandoned lot in Oshawa, Ontario. The basement was a repurposed bottling company located nearby. And the vast majority of the interior was a big, rotting old house in suburban Toronto, which had been closed for decades after serving as a home for single mothers during the Great Depression.

The house itself was creepy even before Muschietti and production designer Claude Paré got to work.

"It was all augmented with really weird safety devices and metal doors, which completely camouflaged the original Victorian style of it, which was fabulous," Paré said. "It was going to be turned into condos, so we had permission to remove everything that wasn’t period and turn it into this fantastic interior, with all the cobwebs and debris and vines growing on the ceilings and furniture."

The house was haunted by several ghosts … including the cranky next-door neighbor, who floated around the set like an evil avenging spirit.

"The worst thing about it was the neighbor, who was a troublemaker," Muschietti remembered. "He basically wanted to make profit from us being there, so he made our lives impossible. He would turn on the lawnmower every time he would hear rolling. He actually got arrested yesterday, the same guy, for disturbing the peace at a shoot in the same place."

The basement of that house was decayed and horrifying in its own right, covered in "crazy-ass paintings of moms with their babies and little squirrels," Muschietti said, laughing. "Nobody wanted to go down there."

Even upstairs was terrifying — and foreboding. "We ripped apart some metal doors and frames and walls, and we discovered under that a little spooky note saying 'You should not have moved all that,'" Paré recalled. "It was really weird. Hopefully nobody will be cursed from doing that."

The Clown Room

When Muschietti sat down in the edit room to watch a rough cut of the film, he felt there was a beat missing during the Losers' visits to the abandoned Victorian. The solution? It needed more scares in the haunted house. So in March, six months after principal photography, Paré built an additional room on a soundstage in Toronto — the only set built after the initial shoot — and filled it with the scariest things they could think of: more clowns.

When Richie (Finn Wolfhard) wanders into the room, he's greeted with a nightmarish circus graveyard, stuffed with decaying, possessed clowns that taunt their petrified young visitor. The clowns' sartorial variety only added to the terror.

"Andy had this concept that he wanted to have clowns from all different eras in the style and fashions," Paré said. "There were real clowns and fake clowns. There was lots of work put into dressing mannequins and putting some heads on them with masks and wigs and so on. Some of them were real people, so they start moving as you see in the movie."

The clowns weren’t the only horrifying flourish. They built a coffin, made custom clown-themed stained glass, and even rented an organ for the day of shooting.

The Cistern

In King’s book, the children trudge through the sewers of Derry until they come across a large, black void, which acts as a portal to a different dimension. But as Paré puts it, "that doesn't really appeal to anybody unless you’re Charlie Rose," so the team had to find a new form for Pennywise’s lair on the other side of the "macroverse," a term King coined for the interconnected universe in which his stories take place.

"Conceptually, I wanted to keep it more grounded and real," Muschietti said. "So instead of going into a crazy world of fantasy, I decided to do a compelling and surrealistic — but still grounded — physical place."

There was another impetus for making the change: budget. As the film had a relatively low budget of $35 million, Muschietti suggested, only half-kidding, that "the creation of that world would have probably sucked all the money from digital effects."

Having decided on more practical and grounded effects, Muschietti and Paré got to work. After trading ideas and designs, they came up with a dank old cistern, which the kids would encounter after traversing the long, labyrinthian sewers beneath the house. Because it wasn’t in the book, there was more freedom to imagine up new story wrinkles, and apply them to the design of the set. It was an impressive construction even with budgetary restrictions, rising to 36 feet high in the studio.

"In the aftermath of Hurricane Katrina, you could see everywhere in town, there were watermarks everywhere, white phosphate marks, and I introduced that in the cistern," Paré explained. "To achieve it properly, you have to use a laser that spins around. You draw a line everywhere. Inside the wagon. Outside the wagon. On the pile of clothing. On the back wall. And on the pipes. You'll see that there's watermarks that are very specifically lined up perfectly well even if the objects are oblique, angled or soft."

The floating pile of kids (and clothing)

Pennywise eats children, but like a weight-conscious diner who pulls the skin off the chicken, he does not consume their clothing. The leftover threads pile up in reverse chronological order, a specification that guided Paré’s set design.

"Given that he started killing people centuries ago, the clothes thing at the bottom would be rotten, a pile of really dark clothes," he explained. "Everything there would be really Victorian, with a little frill or something. Then as you go up, it would be more modern-day clothing. It would be more colorful."

More significant was the reserve of children Pennywise had floating in the center of the cistern. The vortex of dead kids was also a creation born of the combined imagination of Muschetti and Paré, with "floating a metaphor for dying," according to the director.

"It's a vision that so defies physics, very surrealistic and horrifying in at the same time, because you know that all those floating are dead kids," he said. "There's a weird carousel quality to it, which adds to the twisted darkness of it. It's something that kids do a lot, playing. The minute they see a stick they immediately run in circles around it."

One the idea was established, Paré had to get down to logistics. "There were conversations about how many bodies would be floating, conversations even about the speed [at which] the kids were spinning around."

They wound up deciding that there would be enough children to shock the viewer, but nowhere near centuries’ worth of kiddie corpses. That decision would then inform a minor story point.

"We didn't want to go over a year [worth of kids], because all the kids that would have been dead would have been eaten in the 27 years that Pennywise was away," Paré said. "So the kids of that era are basically a reserve for the next 27 years."

A shot cut from the film featured a top-down look at the floating vortex — complete with the children eaten throughout the film floating on top. The movie had enough scares already — and with over $200 million at the box office in just a week, Muschietti will likely have more money to create an even more immersive fright fest for the sequel.