What Is the Upside Down? - How Did Will Byers Get Into the Upside Down?

Three More Questions (and An Answer?) About Stranger Things, by Mary Ellen Iatropoulos

The Upside Down, Stranger Things Wiki

Did Eleven Create The Upside Down? Stranger Things Star Gives Answer

Stranger Things' Upside Down explained: Its origin, Vecna, and more - Polygon

Two Images that Confuse the Upside Down Being Stuck in Time on the Night Will Byers Went Missing : r/StrangerThings

Will You Survive The Stranger Things Upside Down?

Stranger Things Chapter Eight: The Upside Down (TV Episode 2016) - IMDb

SPOILER] How did Will manage to live a whole week in the Upside Down in Stranger Things? - Quora

Hopefully we can get more insight about this in season 5 : r/StrangerThings

plot explanation - How was Will aware of the lights? - Movies & TV Stack Exchange

Will Stranger Things Season 5 Explain What the Upside Down Is