Location from Stranger Things by The Duffer Brothers
A dark, toxic parallel dimension that mirrors Hawkins — a dead world ruled by a hive mind and crawling with predatory creatures.
The Upside Down is Hawkins reflected in a black mirror — structurally identical but biologically alien, a dimension where decay is the only constant and something vast and intelligent watches from everywhere at once. The atmosphere is toxic to humans; prolonged exposure causes respiratory failure. The dimension operates on a hive-mind logic centered on the Mind Flayer, with Demogorgons, Demodogs, and Demo-bats serving as its predatory extensions. Portals between dimensions — gates — can be ripped open by psychic force or by the creatures themselves, and they leave scars that weep biological matter into the real Hawkins. The Upside Down appears frozen in the moment the first gate opened in 1983; time does not seem to pass here in the normal sense. It is not merely a dangerous place — it is a hungry one, and its tendrils have been reaching into Hawkins with increasing aggression. Vecna now commands this dimension, reshaping it with purpose rather than mere instinct.
An exact copy of Hawkins frozen in decay. Every building, every street, every tree is present but wrong — coated in writhing black vines, dusted with floating white spores, and bathed in a sickly blue-grey twilight that never changes. The air is thick and cold, visibility low. Organic membranes stretch across doorways like webbing. The ground pulses faintly. There is no sun, no moon — just a roiling red storm in the sky that flickers with distant lightning. Everything is wet and everything is rotting.
Also known as: The Upside Down, the other side, the dark dimension, the alternate dimension