Arcadia is a realm formed by Dadga for his children to retreat to after he realized that either the fae would break and subjugate the mortals or the mortals would binding and destroy the fae. It is a land of myth and wonder, it hold many strange perils and secrets lost to the ages. The Arcadian natives are the Fae and other unique creature you never want to meet, but many others have made there home here as will such as elves, dwarves and yokai. And as it is a realm of sanction, all are subject to the rules of hospitality.
It is in Arcadia that the Seelie Courts, Unseelie and the Wild Fae hold dominion, but they are far from the only hierarchies.