Welcome to the World of Planescape. Planescape is a campaign setting for the Dungeons & Dragons fantasy role-playing game, originally designed by Zeb Cook. Planescape "solidified the Great Wheel cosmology that began in 1e and would later be reinstated in 5e as the dominant of three theoretical models". Planescape links other Dungeons & Dragons worlds via inter-dimensional magical portals. The game is set in Sigil, the "City of Doors", a torus shaped city/world that rests atop the Spire.