As the name suggests, the Middleworld(s) is a Realm existing between the worlds.
Middleworld consists mainly of the void as well as isles of unformed matter. Every world is born within the Middleworld and every worlds dies inside it .
The Middleworld surrounds the formed worlds seperating one another. Through Sorcery, Magic and Science, Mortals have managed to create passages which allowed them to cross through the middleworld into a different world.
Those Passages usually take the form of a Rift while other times they have the form of an object, like a door, a gate, a House, a Tower and in some cases they are invisible.
The Voidity of the Middleworld, madden any creature remaining within the Middleworld. It has been found out, that casting magic would cause the enmaddening procedure to accelerate.