Short answer: Will Byers ends up in the Upside Down after being abducted by a Demogorgon in the night of November 6, 1983, during a bike trip home from Mike’s place, which leads to his disappearances and eventual discovery in the Upside Down by Hopper and Joyce. Details and context
- Abduction: In the first season, Will spots the Demogorgon and flees, ending up in the Upside Down when the gate or portal effects pull him away from Hawkins. This event marks his disappearance and kickstarts the series’ central mystery.
- Inside the Upside Down: Once taken, Will navigates the dangerous environment, briefly interacting with the Upside Down’s creatures and using improvised signals (such as lights in his home) to communicate. He is eventually found in the Hawkins Public Library, with the Demogorgon having dragged him there.
- Rescue and aftermath: Hopper and Joyce enter the Upside Down through the breached gate to rescue Will, who is physically harmed and connected to the realm via a lingering presence. Will’s experience also has lingering effects in later seasons, including a lasting connection to the Mind Flayer.
- Ongoing developments: Subsequent materials (season 5 materials and fan discussions) suggest Will’s entanglement with the Upside Down continues to influence him and future plotlines, including Vecna’s interactions in flashpoints revealed in new content.
If you’d like, I can pull tighter details from specific episodes or sources to map the sequence of events with exact episodes and quotes.
