Horror movies are built to strike fear and terror into the crowds watching the screen, not usually to freak out the folks making them.

But director Corin Hardy had his own run-in with paranormal activity on the Romanian set of “The Nun,” the newest spinoff in “The Conjuring” series featuring the demonic nun Valak (played by Bonnie Aarons).

An old fortress in the Transylvania region acted as the location for the cloistered abbey in the movie that is being haunted by one seriously unholy lady. One scene in particular finds young Sister Irene (Taissa Farmiga) navigating a long corridor of crosses. Hardy says his imagination ran wild when he read in the script about a long ominous tunnel with hundreds of crucifixes in the script “with a sort of doorway at the end with a message written on it, surrounded by these crosses that have obviously been put there to keep something in or prevent something from coming out.

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“I was just smiling and laughing a lot of the time,” he adds, “because it was actually how I hoped it would look when I sketched it in my sketchbook and now there's an actual demon nun standing there.”

What Hardy didn’t know was the place came with its own resident specters. The story goes that he was ensconced in an old cell along the corridor while the camera rolled. At first he noticed two guys in the shadows, thinking they were just random crew members hanging out, and after about a half hour of takes, Hardy turned to ask them what they thought and no one was there.

“I'm a real lover of all this stuff, but I'm also relatively skeptical in terms of what I've experienced and therefore believe,” Hardy says. “This was a particularly surprising and haunting moment, but it also happened in a working day and I didn't really have time to stop and go, ‘I need to take a break. I just encountered some Romanian ghosts.’ ”

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In the moment, Hardy recalls that he forgot about his ghostly encounter, “and then told people a bit later on and their skin went all goose-pimply. They were like, ‘What?! That just happened today and you didn't say anything about it?’ ”

Now he just wants to give audiences the creeps, and when he first saw Valak in ‘The Conjuring 2,” Hardy knew she had terrifying potential.

“Even if it's scary and in this case demonic, there's something exciting about the prospect of being able to tell a story around (something with) a wickedness to it,” Hardy says. “I've grown up loving monster movies and whether it's vampires or zombies or others, I'm always on the lookout for things that you haven't seen or that are going to take you by surprise.”