Los Angeles, California - Originating as a creepy shared story told online by ordinary internet users, the Backrooms universe erupts into theaters on Friday with a movie directed by star YouTuber Kane Parsons.

The work depicts a group of characters who find themselves trapped in a warren of bizarrely laid-out rooms resembling empty offices, illuminated by a pallid yellow light.

Distributed by A24 – behind multiple horror hits, including 2019's Midsommar – Backrooms mines the unease generated among users of image board 4chan by a strange photo someone posted in 2019.

"I would have been 13 at the time. I do not recall the first time I saw it exactly, because it was very prevalent as a meme," Parsons told AFP.

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He watched as posters' imagination developed the image into a "vaguely nostalgic and vaguely dreamlike but also very tangible science-fiction concept".

The original image was accompanied by a short piece of anonymous text, warning readers against stumbling into its disturbing parallel world.

It quickly became a so-called "creepypasta" – a short horror story reposted and modified around the web, to which other users added details such as monsters and undiscovered dimensions.

"This project is obviously bigger than me," feeding on the input of countless other online posters, Parsons acknowledged.

It was only in 2024 that online sleuths tracked down the original photo to a 2002 renovation of a furniture store in Wisconsin.

Before that, in 2022, Parsons shared a short film to his YouTube channel that he had made with the 3D software Blender.

It depicted a young boy wandering lost through the Backrooms' terrifying corridors.

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Within two weeks, the video had racked up 20 million views.

"I started getting emails from a whole bunch of different companies," Parsons remembers.

"I was 16... it was all very new, and I was very sceptical of what it could mean to try and adapt this or to be engaging with suits" from Hollywood, he added – especially on "something that I cared so personally about".

Parsons finally reached a deal with two production companies and A24, with filming taking place in summer 2025.

British actor Chiwetel Ejiofor plays the protagonist in what became Parsons' first full-length director's credit.

"There was no version of this where I wasn't the one directing that I would personally be open to," he said. "I've always been very stingy about that."

On his YouTube channel, Kane Pixels, Parsons today has more than three million subscribers, with more than 215 million views for the 20 or so videos related to "Backrooms" alone.

The film is "in direct continuity with the YouTube series", Parsons said.

It alternates between "found footage" segments filmed in first person that resemble his web show, and more classic filmic shots.

"It's going to be weird seeing how much [Backrooms] has dropped into the mainstream... Formerly, this has been semi-niche," he mused.

Parsons's work is not the only internet-spawned universe to hit cinemas this year.

YouTuber Mark Fischbach, whose channel Markiplier boasts 38 million subscribers, released the horror movie Iron Lung in January.

The film was adapted from a video game he helped popularize with online clips.

And in 2018, another "creepypasta" about the gangly, besuited monster Slender Man was turned into a feature film that raked in $50 million worldwide.

As for Parsons, "Backrooms is not done", he said.

"I wouldn't rule out film. I wouldn't rule out even television series. That would be my personal hope."

He has meanwhile launched another series on YouTube, The Oldest View, which follows the exploration of an abandoned subterranean shopping mall.