Interesting question, Crystalline =) My Fantasy worlds are sometimes part of the same universe. I know that Watz Eyll and Graceland are two different planets, and not in the same solar system but separated by some thirteen light years. This causes both worlds to have Magic systems that are very different in looks and yet pretty equal in their functions and capabilities. In another story of mine, Wander's Land and Great Britain are connected by magical gateways but otherwise they exist in separate universes. My Aylar worlds are all connected to each other even though they are not the same universe, and it has been established that at least one of them has a connection to the parallel Earth seen in my Joan of England story. Other settings of mine are completely isolated from any other world.