"If you're not careful and you noclip out of reality in the wrong areas, you'll end up in the Backrooms, where it's nothing but the stink of old moist carpet, the madness of mono-yellow, the endless background noise of fluorescent lights at maximum hum-buzz, and approximately six hundred million square miles of randomly segmented empty rooms to be trapped in.
God save you if you hear something wandering around nearby, because it sure as hell has heard you…"

That is how the story goes at least. You never believed, thought it was just some internet fairytale, a myth. That is, until you found yourself there one day. For months there had been rumors of people going missing, sightings of strange entities, even video of people falling right through the floor like a video game. You never believed any of it, but then it happened to you. Now you have to survive in a place rumored to be inescapable. You just hope that the bits and pieces of lore you remember actually mean something...

Update: I added story cards for the first dozen levels.
(Thanks to Lewdleah for auto-cards and purplejump for narrative guidance)

The Backrooms