Shadow Dimensions

The Shadow Dimensions was a realm contained within a flask to which the Doctor banished Fenric in their battle in the third century AD at the conclusion of a chess game. (DW: The Curse of Fenric) According to the ancient Arabian legend of their encounter, the flask contained the Seven Shadows. Like Fenric himself, the Shadows were a remnant of "the time before Time". (DWN: The Curse of Fenric)

The Celestial Toymaker was unimpeded in reaching the location to challenge Fenric to a game. Looking at the grey void and its shifting patterns, he described it as unimaginative, a non-world, and "a dimension of shadows and half-lives." (DWM: Games)

It is possible that the demon who set up Sepulchre as a trap for the Fourth Doctor came from this same realm. If so, then he seems to have escaped in a manner that Fenric and the others couldn't follow. (AG: Demon Quest)