Shredder and Splinter on the rocks of Back of Beyond.
A void beyond time and space, referered to as Back of Beyond, appears in the 1987 TV series episode The Ninja Sword of Nowhere. It consists of some rocks floating around close to each other, and Earth characters can breathe there and protect their bodies without any protective gear.
Krang tells Shredder of extraterrestrial spacecraft using it as a shortcut, to travel between places within microseconds.