At the end of Volume 2, Eleven ( Millie Bobby Brown) agrees to a plan devised by her sister, Eight a.k.a Kali (Linnea Berthelsen) that the only way to really end it, is to vanish into the Upside Down when it's destroyed. That's the only way to ensure the military can't create more children with their powers to use for evil.

“Stranger Things” reached its epic conclusion after five seasons and almost a decade, with an epic battle that took Eleven and company to their breaking point in the Upside Down.