Krang and Shredder watching Dimension Z from inside the Technodrome.
Dimension Z is the home dimension of Mister Ogg, it appeared in the 1987 TMNT cartoon episode "Mr. Ogg Goes to Town"[1] and seems to be a vast wasteland with several planets really close to each other. It was later mentioned again in "The Big Blow Out" by the Shredder when he joked about it after he, Krang, Bebop and Rocksteady wind up stuck in Dimension X again after being stopped by the Turtles again, only for him to be attacked by a angry Krang.
Saturday Morning Adventures[]
In A Far-out Encounter of the Ogg Kind, a bored Ogg decides to prosecute the Turtles for repeatedly breaking the fourth wall. He first sets up a mock trial, but soon gets bored with that, too. Ogg then sends the Turtles to Dimension Z, where he intends on keeping them forever. It is only when Donatello gets an idea that they are able to trick Ogg into sending them back to Earth.