"If you're not careful and no-clip out of reality in wrong areas, you'll end up in the Backrooms, where it's nothing but the stink of moist carpet, the madness of mono-yellow, and 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 hear something wandering around nearby, because it sure as hell has heard you…"

In universe…
Levels often contain sub-levels; levels that are related to their parent level, but are still their own distinct level. They may also contain rooms; locations that are too small to be considered their own level. Usually, they are places in an existing level, but that is not always the case. Rooms and sub-levels are both often referred to as sub-layers.

Out of universe…
Sub-layers are intended to add lore, or "depth" to an already written level. Think of them as spin-offs of the level they can be found in, levels within the level, or a level between two other levels.

Hey, if you're interested in any of these levels, you can always go to the wiki and read them for yourself to find out more about them!
Fandom https://backrooms.fandom.com/wiki/Lev...
Wikidot http://backrooms-wiki.wikidot.com/

OTHER COMPILATIONS:
Every Level    • Every discovered normal level of the ...  
Every Level (Cluster II)    • CLUSTER II - Every discovered level o...  
Every Secret Level    • Every secret level of The Backrooms (...  
Every Negative Level    • Every discovered NEGATIVE level of th...  
Every Entity    • Every entity of The Backrooms (UPDATE...  
Every Object    • Every object of The Backrooms  
Every Joke entry    • Every Joke Level and Entity of The Ba...  
Liminal Archives    • Every Limspace of The Backrooms & oth...  

MUSIC USED:
"Libet delay" by The Caretaker    • Libet delay - The Caretaker (Stage 3)  
"~" by Happy Trendy (slowed down at 0.9x)    • ~  
"Dusty Tapes" by YG HYPNOS    • Dusty Tapes  
"Back There Benjamin (Libet's Delay / All Joy Camaraderie) Remake" by Music Lover2 (Original songs by The Caretaker)    • The Caretaker - Back There Benjamin (...  
"Vas" by Jagger Finn    • Vas  

DISCLAIMER: Every image showed in the video comes from the Backrooms Fandom Wiki (almost all of them).
All of them belongs to their respective owners
Some images were edited by the level's autors

0:00 Intro
0:05 Fandom Sub-Levels
8:42 Wikidot Sub-Levels
16:08 End