The Bad Place
"The Bad Place" is a world in an alternate universe which dreamwalker Kaia Nieves is inexplicably drawn to, calling it "the Bad Place." The dominant species of the word appears to be large kaiju-like creatures, though smaller humanoid figures appear to exist as well.
Kaia Nieves can see into other worlds by dreamwalking. One of these worlds, which she has dubbed "the Bad Place," was the only world she would visit in her dreams. It is a place of blood, death, and monsters. Any injuries she incurs in the Bad Place follow her into the waking world, causing Kaia to take amphetamines to stay awake.
Jack tracks Kaia down on the suggestion of Derek Swan, because he thinks she can help him rescue Mary Winchester from the Apocalypse World. Meanwhile, Patience Turner has visions that involve flashes of the Bad Place, where Sam, Dean, and Jody are being attacked.
With angels pursuing them to try and capture Jack, the Winchesters, Kaia, and Jack are cornered in an abandoned ship. In a last-ditch effort to escape, Kaia and Jack try to open a portal. Kaia takes a seat as Jack places his hands on her head and as the energy flows between them, Kaia is taken to the Bad Place, but with Jack's help she is able to pull away into the multiverse, where he is able to locate Apocalypse World. As the two mentally traverse the post-Apocalyptic landscape, they are able to reach Mary Winchester's prison. But Kaia's connection begins slipping, sending them back to the Bad Place, where a cloaked figure is stalking through the woods. Jack tells her to focus, bringing them back to Apocalypse World, until the strain becomes too much and Jack and Kaia send out a blast of energy that disintegrates the angels, sending Jack to Apocalypse World and Sam and Dean to the Bad Place. Regaining their composure after being transported, Sam and Dean begin exploring where they are, and unbeknownst to them find themselves standing in a gigantic footprint as a loud monstrous roar echoes through the land.
Having been transported to the Bad Place, the Winchesters attempt to find a way to escape while avoiding the monsters that roam the world. They are eventually captured by a hooded figure who ties them to a tree to feed Sam and Dean to the Kaiju.
In the Winchesters' world, Jody Mills attempts to find Sam and Dean with the help of Claire Novak, Alex Jones, and Patience Turner. At Sioux Falls General Hospital, Claire is able to locate Kaia Nieves, who is attacked by a creature from the Bad Place after fleeing outside. The creature is killed by Claire and Jody and a dissection is performed by Alex. Kaia explains her visions of the Bad Place to the group and her efforts with Jack to open a portal to Apocalypse World that had gone wrong. The group realizes that the portal had instead connected to the Bad Place and that it is still open, which is how the creatures were able to pass through.
After an attack on Jody's house, the group tracks down the portal with the help of Sheriff Donna Hanscum. Under attack by several of the creatures, Jody, Donna, Alex, and Patience hold them off as Kaia and Claire pass through the portal, which is closing, to the Bad Place to rescue their friends. Claire and Kaia free Sam and Dean, but at the portal are ambushed by the hooded figure who throws her spear at Claire, killing Kaia instead when she gets in the way. With the Kaiju approaching and the portal closing, Sam and Dean drag Claire back to their world, leaving Kaia's body behind. The portal closes moments later behind them while Jody's group has managed to eliminate the attacking creatures.
In the aftermath, Sam warns Jody that the portal to the Bad Place was open for a few days and thus more of the creatures may have made it through in that time. Jody promises that her group can handle any that are left while the Winchesters focus on saving the world. That night, another portal opens from the Bad Place in a Sioux Falls park and the hooded figure emerges, revealing herself to be the alternate Kaia.
After seeing the figure in Dean's memories that hurt Michael enough to force him flee Dean's body, the Winchesters recognize it as the being from the Bad Place that had killed Kaia Nieves. After tracking her down, they learn that she is the Bad Place version of Kaia who refuses to reveal how she was able to reach their world from the Bad Place. The alternate Kaia explains that she too is a dreamwalker and has been sharing visions her whole life with their Kaia which is why Kaia had so many nightmares of the Bad Place throughout her life.
After Dean and Castiel catch up with her, Dark Kaia expresses a desire to return to the Bad Place, which she calls her home. Though Dark Kaia had initially fled the Bad Place to get away from her life of constantly running from monsters, she has decided that she wants to return after being hunted relentlessly by Michael's Monsters. Dark Kaia explains that she used magic from the Bad Place to open the portal between the Bad Place and the Winchesters' world, but that same magic doesn't work in the Winchesters' world. Instead, Dark Kaia offers to trade her spear for the help of Jack Kline in returning home once Michael is defeated. Dean agrees, promising to help Dark Kaia get back to the Bad Place where she tells them that she has people she cares about and wants to protect, the same as them.