Phantasm Zone

The Phantasm Zone is a prison dimension within a dimension that flies through the Twisting Nether forever, its occupant able to see out, but never escape. It was crafted by the Kirin Tor to imprison Magnus Manastorm, who had the impossibly rare problem of being more dangerous dead than alive.

Trivia

 * Its description seems to follow the same one as pocket dimensions.
 * It is a reference to the from DC's Superman stories, a pocket dimension used to imprison dangerous criminals.