Annwn (Annwfn, Annwvyn)

   A probable name for the Celtic Otherworld (underworld). An early Welsh poem attributed to Taliesin, Preiddeu Annwfn, tells how Arthur led a raid there, apparently to carry off the cauldron of plenty. The expedition sailed in the ship Prydwen to the fort or city of the Otherworld Caer Siddi (Caer Rigor), but only seven returned. The language of the poem is obscure. The expedition of Arthur to Ireland in Culhwch may be another version of this story.
   In the Mabinogion, it is the land ruled over by Arawn. As another site pointed out, Annwn is not considered to be a place of punishment or eternal lamentation; it is rather a place of ancestral power which mortals may visit, and from which the Wild Hunt rides out.