The Chronicles of Amber
Many of Zelazny's works explore variations upon the idea that if there exists an infinite number of worlds, then every world that can be imagined must exist, somewhere. Powerful beings in many of his stories have the ability to travel to worlds that possess precisely the characteristics which that being wishes to experience. (Zelazny characters with this ability include Thoth in "Creatures of Light and Darkness", who teleports to these worlds; those with the royal blood of either Amber or Chaos in "The Chronicles of Amber", who "move through shadows" to reach these worlds; the guardian families of "A Dark Traveling", who move between realities using high-tech devices; and Red Dorakeen in "Roadmarks", who reaches these worlds by driving along a magical highway.) Many of these same characters wonder whether they are creating these special places anew, or are merely finding places which already exist (very much like "the problem of universals" in classical metaphysics). Usually each character who ponders this ultimately decides that the question is purely academic and therefore unanswerable.