The Far Realm is a Lovecraftian-like eldritch dimension from the fictional universe of the Dungeons & Dragons pencil-and-paper roleplaying game by Wizards of the Coast.
The Far Realm is a plane of madness, which is very far from the material plane. Which consists of an infinite number of layers of finite size. Layers that are very thin from a mile in thickness at most to an inch at the thinnest, with 10 ft separating each layer. Which are transparent and highly morphic. Entities and landmarks within the Far Realm are multidimensional, simultaneously existing on multiple layers at once.
It's a plane with forests of tentacles vegetation, viscously syrup-like air, drifting colossal multi-layer beings with the smallest being city-sized, falling globes that burst releasing horse-sized ticks, rivers of mikly white fluids, etc. Neither time or gravity exists in the Far Realm. Inhabited by a number of species including Aboleth, Illithid, Beholder, kaorti, and carrion crawlers. Many Aberrations are also created here. Visitors usually go mad and all are twisted into gruesome creatures. It threatens all of the realities in the Multiverse. The rulers of the Far Realm are the Uvuudaums, whose very presence would make most creatures insane.