Nichtschwert and me wrote up a proposition:
What is currently known as the Void, accessible by destroying the Trap Room in your dreams, is actually the mere surface - the shore of a much deeper ocean. The actual Void, resting below, is a black sea of thoughts made manifest and material, where terrors and dangerous knowledge can be found. Only occasionally does something bubble up to the surface, which leads to the disturbing visions sometimes reported after a Dream Cleansing. While human consciousness floats at the Shore, entities banished in a Dream Cleansing weigh heavy and fall into the Void.
The dreamscapes - the place where your consciousness stays while it dreams - are usually located at the Shore, with the Trap Room being the bridge between the dreamscape and the Shore. But certain events, often of paranormal nature, can unhinge your dreamscape enough to start floating into the Void.
The Corridor of Darkness actually leads through a part of the Void which temporarily manifests itself physically. If the connection of two rooms should, by chance, lead through stairs, you will encounter those stairs in the Corridor. If you should walk upwards, you will end up at the Shore, where dreamless sleepers rest.
When a person falls unconscious, their consciousness usually ends up in the Void. Normally, they will lose time and not remember anything in their brain's valiant effort of protecting itself from terrible knowledge.
If one's soul has been sufficiently torn apart by paranormal influences, shards of their consciousness can get stuck in the Void, even long after their death. It is possible to free them from there, although it hasn't been necessary in a while.
EDIT: Is there no feedback? Does that mean you guys are cool with this or not interested? °3°