In the Dungeons & Dragons fantasy role-playing game, Arcadia (/ɑːrˈkeɪdiə/ ar-KAY-dee-ə) or more fully, the Peaceable Kingdoms of Arcadia, is a lawful neutral/lawful good-aligned plane of existence. It is one of a number of alignment-based Outer Planes that form part of the standard Dungeons & Dragons (D&D) cosmology, used in the Planescape, Greyhawk and some editions of the Forgotten Realms campaign settings.
Arcadia is a peaceful harmony between law and good and is noted for its tranquility and strict discipline. Everything on Arcadia has its specified place and everything functions as intended. Trees naturally form tight rows in orchards and streams snake across the perfectly flat plains in complex mathematical routes. Large geometric cities are perfectly laid out with efficient roads and beautiful architecture.
The Orb of Day and Night is a huge sphere that sits atop the tallest mountain in Arcadia, one side is illuminated and the other dark. The orb rotates at a constant speed so that exactly half of the plane is in darkness while the other half is illuminated. There is no dawn or dusk on Arcadia, but a sudden sharp change. The weather on Arcadia is always pleasant and seasons are of exactly equal length, which like the days, change abruptly when it is time.