Many say the Red Dimension does not exist. Those people are the ones who have only heard about it through written or spoken word. Those who have experienced it will say otherwise.
This dimension is unlike any other. For starters it is red. Everything is red. Secondly, it is made up entirely of code.
Over the years people have guessed at it being a simulation, or even what our world is built upon. Neither of these is true. In simple terms, it is a living world that has grown up around, or rather, underneath, ours and has copied as best it can what our world looks like. It is not a simulation, despite that being what it could look like. It's not simulating anything other than looks. The populations, cultures and species are all it's own design.
It's rare for this dimension to break into out world, being as they are not compatible to exist together. Most times it does break through, however, will be in deep space rifts such as black holes or a momentary glitch in reality that gives the impression of things being ever so slightly different than they were before. Some places and branches have figured out how to open and keep open a communications to this dimension and have so far used it well. The Hub uses it to send instant messages throughout the Complex and OU1 has tapped into the potential of codegraphs, a system that allows hyperrealistic holographs to be made.
In a graveyard on an abandoned part of OU1 a window opened up that revealed the Red Dimension. It was a literal window floating in the middle of the air, frame and all. It wasn't discovered for a long time and once it was cordons were installed to keep any public away.