The Official Trailer:

If you’re not careful, you could noclip into the Backrooms.

There are LOTS of Levels

Requirements:

Iris (with Sodium) and the shader pack IterationT 3.2.0 - the mod asks you to enable it before you play.

                                          Credits

Made by Haecker.3
Inspired by The Backrooms, the internet folklore that started in 2019, and the many stories the community has written
about it.
SCP-106 and SCP-939 are based on the SCP Foundation (scp-wiki.wikidot.com),
licensed under CC BY-SA 3.0.
Several creatures and places (the Smiler, Hounds, Skin Stealers, Deathmoths, the M.E.G. and many levels) are based on the
collaborative Backrooms fiction of the Backrooms Wiki (backrooms-wiki.wikidot.com),
licensed under CC BY-SA 3.0.
Some levels were inspired by the game Escape the Backrooms. This mod is a fan project and is not affiliated with any of
these projects.