The Backrooms

The Backrooms are a parallel dimension, which can be entered by noclipping out of reality in "a wrong area".

They are inhabited by a strange entity referred to as It or the Being.

Characteristics
The known Backrooms consist of approximately 600 million square miles of randomly segmented, mostly empty rooms.

The rooms' walls are covered with yellow and ornamented wallpaper and the floor consists of a damp gray-ish yellow carpet. The ceiling is mostly made of white ceiling tiles, with fluorescent lights scattered across it. Vents can sometimes be spotted, making a humming sound. Splatters of dark substance can sometimes be found on the ceiling or on the walls.

The ambience inside consists mostly of the buzzing of fluorescent light bulbs.

Lights
The lights are the only source of light in the backrooms. Most of them work, defective can be found however. Their placement is irregular, varying from being very far apart to right next to each other.

A ceiling tile supposedly containing a light can sometimes be seen removed, exposing the black void outside of the backrooms. Said occurrences are a sign of the presence of It.

Walls
The walls create the bizarre structure of the backrooms. They are fully covered in yellow wallpaper, seldom containing empty door frames. Rarely walls can offer an exit out of the backrooms. Sometimes stains of dark substance can be observed, presumably caused by the presence of It.

In-game
In-game, The Backrooms are a procedurally generated infinite area that matches the original description.

The player enters The Backrooms presumably by carelessly noclipping in a wrong area. Scarce exits allow The Player to escape The Backrooms, once found.

Once in, The Player's sanity will start to deteriorate and It will start hunting them.

Exiting
Occasionally, the player will stumble across intense visual glitches on a wall that match the entrance, which give out a low rumbling noise. Those are the exits that allow the player to escape.

Once interacted with, the player will have to "calm themself" down before exiting, by playing "The Calming Game".

The Calming Game is a bar with a moving line across it and a beating heart. The player must "calm themself" by interacting with the heart when the moving line flies across it. Successful interaction (green bar) will actually not affect the madness level but will allow you to exit, while missing (red bar) will increase it. The Calming Game becomes harder the more insane the player is.