Stranger Things season 4 is on the horizon, and so far, eight known characters have visited the Upside Down. A few of those figures didn't make it out alive, but those who did were able to gather key information about the alternate dimension. Much of the parallel world still remains a mystery, which is why scientists from across the globe are invested in the Upside Down. Unfortunately, one of the key "Gates" resides in the sleepy town of Hawkins, thrusting a handful of citizens into a world they can barely comprehend.
The Upside Down mirrors the human world but houses a superorganism known as the Mind Flayer. Through the control of a hive mind, the Mind Flayer controls the alternate dimension, including a group of creatures called Demogorgons. After a young girl with telekinetic abilities tapped into the Upside Down and made contact with a Demogorgon in season 1, a rift opened. While the Demogorgon was able to pass into the human world, Hawkins citizens had the opportunity to pass into the dark dimension.
Not all who entered the Upside Down did so under their own power. When the Demogorgon found a new victim, it would often drag them into the dimension. Mike Wheeler, Dustin Henderson, Lucas Sinclair, Max Mayfield, Steve Harrington, and Bob Newby all came close to entering the Upside Down. The group explored the Hawkins' tunnels, a location near the Gate that acted as a medium to the dimension. Even the characters who successfully escaped were haunted by the parallel world and even acquired dangerous side effects. Here's a breakdown of characters who entered the Upside Down through season 3.
Will Byers
Young Will Byers was the first person to unwittingly visit the Upside Down. After playing Dungeons & Dragons with his friends, he embarked on the trip home only to be abducted by the Demogorgon and taken into the alternate dimension. The disappearance of Will set off the events of Stranger Things. Somehow, Will managed to evade the monster while surviving in the mysterious dimension while his family and friends searched for him. He's eventually rescued from the Upside Down when he was found unconscious with a tendril down his throat, which was just the beginning of the dimension's control of him. Months later, Will was coughing up slug-like creatures and the following season it was revealed that the Mind Flayer chose Will as its new host.
Barbara Holland
As the best friend of Nancy Wheeler, Barbara Holland was often dragged to events that she had no interest in attending. After accompanying her friend to Steve's house, Barb was attacked by the Demogorgon and taken to the Upside Down. Days later, Eleven searched the Upside Down through her psychic abilities and discovered Barb's corpse, confirming the teenager's death. Barb's disappearance was covered up by Hawkins Laboratory before Nancy outed their involvement, assisting in the facility's shutdown and providing the Holland family with closure.
Shepard
In the Stranger Things season 1 episode "The Body," a scientist working at Hawkins Laboratory entered the Upside Down on a test run. The character named Shepard donned a hazmat suit and entered through the Gate in the lab while linked to a chain. The scientist was reporting his findings over a shared radio just before the Demogorgon got to him. His crew tried to pull him back but only a bloody piece of the suit was left on the chain.
Nancy Wheeler
Nancy felt an extreme amount of guilt for Barb's disappearance since she forced her friend to attend Steve's party. While investigating with Will's brother, Jonathan, the two discover the truth regarding the Demogorgon's existence. They formulate a plan to kill the creature, but first, Nancy followed it through a Gate found in the woods. After the Demogorgon discovered her in the Upside Down, Jonathan was forced to frantically retrieve Nancy. Though she survived, Nancy was greatly traumatized by the event.
Jim Hopper & Joyce Byers
The Chief of Police in Hawkins, Jim Hopper, and Joyce Byers, Will's mother, teamed up to investigate the truth about the young boy's disappearance. With the help of the kids, especially Eleven, they discovered that Will was alive but trapped in the Upside Down. Hopper and Joyce broke into the lab since the Gate was located underneath the facility. They negotiated a way to get inside before donning special suits and scouring the dimension for Will's whereabouts. They eventually find Will, but were forced to resuscitate him through CPR since he was attached to tendrils. The pair then got the boy out of the dimension and back into the human world.
Eleven
After Will was rescued, the Demogorgon set its sights on Eleven. The two powerful beings faced off in the local middle school, where Eleven's full potential came to light. While Eleven disintegrated the monster, she was transported and trapped in the Upside Down in the process. Eleven's escape from the Upside Down wasn't revealed until Stranger Things season 2, but by then, her friends thought she was dead. She found a tear in the Gate located within the high school and broke through. Since special agents were trying to capture her, she was then stuck living on her own until Hopper stepped up as her primary caregiver.
Billy Hargrove
So far, Billy Hargrove was the eighth and final character to have a direct connection to the Upside Down in Stranger Things. After crashing his car at the start of season 3, Billy found himself outside of Brimborn Steel Works. He investigated the area before being dragged inside by the Mind Flayer's power. The mega-monster then marked the teen as a host by infecting his mind. When Billy tried to escape, he envisioned himself in the Upside Down before he was instructed to build the Flayed army. Throughout the rest of the season, the Mind Flayer was in full control. The character was killed by the same monster that first affected him, but there's still plausible ways Billy could return in the series.