The Dream World is the communal place where all people have their dreams, but most are not conscious of this fact. The dream world tends to follow the realities of the real world, as the dreamers bring that knowledge with them into their dreams, but a person can have a great deal of control in the dream world based on a combination of willpower and imagination. This is why magic is possible for many more people in dreams and why it is much harder for a mechanical device to work—the creator has to be able to picture every part and motion, and that includes at least a basic understanding of the combustion reaction involved in bullets, or gas engines.
Because it is a world powered by imagination, many people have vastly different environments here. One can also easily change their surroudings by imagining something different, and this may create a constantly changing or morphing "reality," as one may notice in their dreams.
Several people accompanied Raihosha to the dream world to help him defeat The Traitor, and they enjoyed a rather scenic tour of the place before getting down to business. Their travels included a town where cats are greatly revered, as they have special powers related to the moon. Artemis, as a cat, was able to create a bridge which the party used to get to the moon.
Raihosha frequents the dream world, and has great control there. He can operate vehicles, etc., and Eiry has also learned to control her own dreams to a certain extent.