What is the alternate dimension called in Stranger Things?

The alternate dimension in Stranger Things is called the Upside Down.

The Upside Down is a hostile parallel version of Hawkins, Indiana. It resembles the town’s streets and buildings but is covered in darkness, spores, vines, and organic growth. The dimension is also inhabited by dangerous creatures connected to the series’ supernatural mythology.

The name is used by the characters as an accessible description rather than as a scientific classification. Early seasons present it primarily as a mysterious place linked to Will Byers’s disappearance and the Hawkins National Laboratory experiments.

The Upside Down is often confused with the Mind Flayer, Vecna, or the broader supernatural forces in the series. Those are entities or characters associated with the dimension, whereas the Upside Down itself is the parallel environment. Its mythology becomes more detailed as the seasons reveal additional connections among Hawkins, Eleven, and Henry Creel.