Planescape is a campaign setting for the Dungeons & Dragons role-playing game, known for its unique multiverse structure. It features the city of Sigil, a central hub that connects various planes of existence, allowing characters to travel between different realms, each with its own rules and inhabitants. The setting emphasizes themes of philosophy, belief, and the nature of reality. Players can encounter diverse creatures, including modrons, tieflings, and githyanki, while exploring the intricate relationships between the planes. The rich lore and complex politics of Sigil provide endless opportunities for adventure and storytelling.