The Zone of No Return was a dimension where the rising Time Lords banished Fenris, agent of the Order of the Black Sun, after his sabotage of their conquer of time travel. It shared some relation with the time vortex; indeed, chaos of "raw time" characterised it. It could be accessed by the Void Mouth, wearing space suits and "head bubbles".
After twenty years of exile, Fenris was supposed to have been broken into living splinters, scattered through times. Rema-Du trained for ten years to access the Zone and retrieve him. She was escorted by the parahuman Wardog, whose mental strength enabled him not to lose his mind while in the Zone. Eventually, they managed to rescue Fenris. (COMIC: 4-D War)