The Beginning appears to be an office room that has a single laptop with lines of code running on it. It has been claimed that you are able to edit the code to alter the shape of the backrooms. The room itself have no walls, and the floor appears to be infinitely stretched into the horizon, but the place has only a light bulb hanging in the air and thus visibility is low. The computer can alter the properties of certain rooms but cannot affect it in large quantities, such as deleting a room or deleting an entity.
That is all that has been reported, further study is being conducted by B.A.S.
The exit point is fairly easy, either run a 'spawn' command to spawn the train from the Metro (beware that don't accidentally spawn entities instead) or no clip at the invisible barrier that instead of taking you to the negative levels, will take you to level 0. The entry point into The Beginning is kept a secret and anyone found talking loudly about it would be killed either by entities or T.T.G Mercenaries.