Therefore, its known narrative elements are not a part of the Doctor Who universe. It may have been the basis for a similar story in another medium, however — and that story may indeed be a part of the DWU.
|The Dark Dimension|
|Companion(s):||Ace, the Brig|
|Format:||Unproduced direct-to-video film|
|Unproduced Doctor Who TV stories|
The Dark Dimension, written by 'fan scholar' Adrian Rigelsford, was a planned direct-to-video film commissioned by BBC Enterprises that was to have been released in 1993 to commemorate the thirtieth anniversary of Doctor Who.
- According to Rigelsford, "Tom Baker went to the BBC and said 'I would like to be Doctor Who again', and that's the reason why it happened." Apparently Baker even suggested Douglas Adams as the script writer. 
The Dark Dimension (later known as Lost in the Dark Dimension ) ran into obstacles which prevented it from being produced, large among which was that BBC Enterprises was in charge of generating revenue, not producing films. It therefore lacked facilities, staff and experience in producing something like The Dark Dimension.
- ...November 1992, BBC1 Controller Jonathan Powell heard of the project and objected to Enterprises making the production on the grounds that it was a marketing wing of the BBC and not a drama production unit. 
Actor availability was another of the problems which faced the production which began at some indeterminate time in 1992 (with an aimed release date of November 1993). Scheduling all the surviving actors who played the Doctor (Jon Pertwee, Tom Baker, Peter Davison, Colin Baker and Sylvester McCoy) up to that point would have been incredibly challenging and almost impossible considering the set date of release. Finally when Philip Segal (then part of Amblin Television) joined with Universal Television to co-produce a new TV series of Doctor Who (for the American Market), BBC Enterprises had to pull out of the project due to a conflict of interest. 
Some of the actors, particularly Jon Pertwee and Colin Baker, were not pleased that their roles were so small (the script featured the Fourth Doctor prominently while the others had cameos). 
The story would have centred on an older version of the Fourth Doctor, the Brigadier and Ace with shorter appearances by the other surviving Doctors, though in more minor roles. Classic monsters would have included the Cybermen, Daleks, the Ice Warriors and the Yeti.
The central idea to the story was that of the alteration of time by an evil creature so that the Fourth Doctor would not have died and regenerated after falling from the Pharos Project (as seen in Logopolis). In doing so, the creature created a "Dark Dimension". The Doctor had to revert back the timeline before he and his future incarnations were erased from time by the effect.
Along with the inclusion of almost all the classic monsters, many of them were to be redesigned or feature totally new developments of the original design.
- "'The Cybermen were not like any we've ever seen before,' says Rigelsford. 'There was a specific Cyberman who was being made by the people at Henson's Creature Workshop. The guy who designed it was Chris Fitzgerald . It had holes in its knuckles and there was a point where it held up its hand, made a fist, and six-inch blades shot out of its knuckles! It was like Wolverine out of the X-Men comics; Cyberrine!'"
The Daleks also were to have featured a redesign featuring a new special weapons Dalek.
- "'The Daleks were going to have laser-guns that were going to be done with computer animation so the laser bolts would be in 3-D rather than just going 'Zap!' with a blue line. The bolts were going to be like spears coming out in 3-D.'" 
Graeme Harper was scheduled to direct the story.
- "About three weeks worth of test filming was done including model and titles effects, and some location filming was also undertaken. 'We were going to go down to Shepperton film studios,' says Rigelsford, 'and have it shot on film on one of the largest sound-stages on Shepperton.'" 
Adrian Rigelsford wrote a book entitled The Making of the Dark Dimension which contained scripts and concept drawings. However, it repeatedly ran into release problems and has never been released.  The Dark Dimension and its production were briefly mentioned in Rigelsford's own Classic Who: The Harper Classics.
- Short Synopsis taken from The Nth Doctor of The Dark Dimension
- NZDWFC - TSV 44: "Inside the Dark Dimension" by Jon Preddle