A place of mono yellow, smelly moist carpets, the loud buzzing sound of fluorescent lights, and about six hundred million square miles of randomly segmented empty rooms. People who aren't careful and noclip out of reality in the wrong places can end up in The Backrooms, where they can spend hours to years trying to find the way out, as time there is absolutely distorted. Oh, and it can happen to anyone, at anytime. And to top it all off? This is the tutorial level!
Level 6: Lights Out, where you are trapped in pitch black halls, with no idea how big the level is due to how dark it is, and you start encountering Insanities and hallucinations. Oh, and no light sources you have will work on this level.
Green Antarctica: The glacier at the center of the continent is seen as one by the Tsalal, one so evil that they refuse to give it a name. While their entire culture fears the color white, it goes beyond just that. The glacier is the size of a country and half a mile thick. The dry, chilled air above it is unnaturally lit by the sun and carries sounds differently, giving it the feeling that reality is warped by its very presence. The entire thing moans and creaks as fissures open up and water erupts outward. Its edges expand and retreat like the pseudopods of a vast amoeba. There are times when the winds will trigger a sudden torrent of frigid air that splashes outward and kills everything in its path. The Tsalal cultures alternatively view it as the source of all death and suffering, hell, the abode of the gods, or even a sleeping god itself. What they can all agree on is that, when it awakens, it will bring about the end of all worlds.
The Noisy Tenant Creepypasta Mythos is very much set in this this, given that in the core premise is that people suddenly wake up, out of nowhere, in the titular building, an endless place where space and time, if the ending to Dr. Phage's Hospital is any indication doesn't work the same as in our reality and where there's been no exit shown in-setting. The place itself can be described as what would happen if Silent Hill were designed by Sid and Marty Krofft Productions , with whimsical inhabitants (An anthropomorphic hamburger chef made of rotting meat and a man-sized bacteriopage doctor with glasses and a bow-tie being the most prominent) who do horrible; horrible things to the people stuck in their realms... And, as a bonus, the creator has said that it's not anything as banal as another planet or another dimension, but rather something humankind has no context whatsoever for. He compared trying to explain the reason why it exists to explaining to a Pilgrim the concept of a YouTube Poop without explaining computers, videos or electricity.
Protectors of the Plot Continuum has Headquarters, an unimaginably huge building located in the space between worlds that the PPC calls home. It's constructed from metafictional materials like Plot Holes and "concrit" (concrete made from constructive criticism) and a portal to it exists in one specific location in each world of The Multiverse, usually an extremely innocuous one nobody would check if they weren't specifically looking for it. Its most famous feature is that, as a defense against attacks, it's impossible to intentionally find your destination within it; PPC agents are well trained to "switch off" their minds whilst trying to get from one part of the building to another, something the simple brains of Sues are incapable of. A Running Gag in the stories is that it supposedly has a pool, but nobody, whether intentionally or not, has ever been able to find it.
There's the "Red Sea Object", which takes people into an alternate universe where "a god-like being of unknown origin" instigated a massive holy war hundreds of years ago, with apocalyptic results, and now giant, immortal monsters roam the land, absorbing anyone who catches their attention.
According to this tale, SCP-354 leads to a world like this. Days last 43 1/2 hours, the sun is bright red, and the laws of physics don't seem to be consistent. Compasses shift daily and liquid water exists alongside liquid carbon dioxide. And there's also the heavy implication that the world can erase people from existence.
SCP-1372 is an anomalous stretch of ocean. For anyone moving across it going from west to east, it seems normal. Moving from east to west, though, it'll seem like they've come to the edge of the world. The closer they get, the more of a compulsion they'll have to continue on over the edge, at which point they'll disappear from sight and all tracking software. Occasionally, ships and even planes that have vanished in the area have returned, able to move despite being so damaged that it should be impossible, and try to convince others to go over the edge. One of whom is heavily implied to be Ferdinand Magellan.
SCP-1730, or Site-13, is a Foundation site from an alternate universe where anomalies were experimented on and executed via incineration. This... didn't turn out well, and the site ended up in the main Foundation universe in a heavily damaged state. The spatial topography of the place is unstable, so you might suddenly find a wall where there used to be a corridor. The physical structure of the place is also unstable, so you might suddenly have the floor collapse underneath your feet. Then there's the creatures wandering around, like an entity that draws cognitohazards on the walls, and the leeches that forcibly enter people's bodies to take control of them. The last we see of the place, it's shifted into another reality during a brawl between a god, the archangel Uriel and a giant leech-thing, all of which were imprisoned there.
SCP-1936 is Daleport, a small town in the northeast United States. At least until an Apocalypse Cult decided to host a Divine Conflict for several demons to free-for-all against each other. Now the air is thick with fog and the buildings bleed ashes.
Alagadda is a city located in some sort of pocket dimension or world between worlds. It can only be accessed via various alchemical methods, and appears to be a Portal Crossroad World, though not to the same extent as the Library. Time spent there feels like a dream, randomly sped up and slowed down, and it's ruled over by the Hanged King, with the implication that he's nothing more than a puppet to the Ambassador of Alagadda.
Corbenic is another anomalous alternate world. It is said to be an afterlife, and it has three "moons" hanging in the sky... each of which is an alternate Earth that has somehow been absorbed entirely into the realm. The descriptions of what happens to people in various regions within Corbenic are... disturbing, especially since the victims cannot die.
SCP-2922-Bnote A woman who entered Corbenic after death but was still able to contact the Foundation: This is not Heaven, not Hell, not Purgatory... this is the final exam.
SCP-3930 is a region of pure nonexistence. Somehow, it does not have any size or border, but it is at a fixed location on Earth and people and beings can "enter" it, which makes them cease to exist as well. You Cannot Grasp the True Form is in full effect, people and even electronic recordings just see it as more of its surroundings as part of the mind's attempt to see patterns where there are none going into overdrive. The same "attempt to see patterns" also causes hostile beings called Pattern Screamers to form, which are nonexistent as well but self-aware at the same time and hate their borderline extant/nonextant state of being. The void itself does not make them, peoples' minds do. The only known way to stop that from happening is to have the total existing number of those aware of SCP-3930 not exceed ten.
The Sick Land revolves around such a location. The titular Sick Land is a massive patch of land where strange plant life grows; people and animals that stay there for too long suffered bizarre, incurable, and fatal mutations and sickness. Later it's revealed to be spreading at a slow rate, corrupting the land around it.
The Sugar Bowl is a strange form of this. It may be depicted as a genuinely nice place, or as it was in the article. However, there's no denying that a place with licorice trees and structurally sound buildings of candy would belong here.
The Clown-Car Base also fits this trope in a way, especially when the trope is lampshaded, revealing it to be not just a perspective oddity, but a genuine physically disproportionate building.
A Level Ate is a place where terrain is Giant Food, often a humorous version of this sort of thing.
A Dark World can function as an Eldritch Location when it's explicitly evil or "wrong", but a few morality neutral Dark Places are natural "night side" reality counterparts to our own.
The Fineum Cuniculum from The Worldbuild Project probably qualifies. No one knows how it got there? Check. Mysterious engraving all down the walls of a three kilometer tunnel? Check. People randomly disappearing? Check.
Belfry Books in Sibylline Sounds breaks all manner of conventional reality in some way or another. It's Bigger on the Inside to the point of having multiple biomes in it and possibly even going on forever, it extends into other dimensions & points in time, and it's likely a Genius Loci as well. There's also the fact that it can transform those who enter it into different forms, and if a person owns it for long enough then they can be imbued with magical powers, as is the case with its current owner Oreo. It's theorized that the bookshop's magical nature may stem from it being built on top of another Eldritch Location, a magical ley line deep beneath the ground, but this is only one theory.
, which takes people into an alternate universe where "a god-like being of unknown origin" instigated a massive holy war hundreds of years ago, with apocalyptic results, and now giant, immortal monsters roam the land, absorbing anyone who catches their attention.