Steve Rose Chiwetel Ejiofor has been on a lot of movie sets, but Backrooms was something different: a 30,000 sq ft labyrinth of apparently random corridors and chambers, all carpeted, fluorescent lit and decorated in the same sickly yellow wallpaper. It was so big that people were getting lost in it, says Ejiofor: “Especially on those first days. As you try to navigate your way around and you're like: ‘I'm sure it's this door, I'm sure that's the way.'” He's laughing at the recollection.