
1) Celtic girl name 2) Imaginary place 3) Mythical place 4) Otherworld 5) Welsh mythology
Found on
https://www.crosswordclues.com/clue/annwn

Annwn (also spelled Annwfn or Annwvyn, in Middle Welsh Annwvn, Annwyn, Annwyfn or Annwfyn) was the Otherworld in Welsh mythology. Ruled by Arawn (or, in Arthurian literature, by Gwyn ap Nudd), it was essentially a world of delights and eternal youth where disease was absent and food was ever-abundant. It became identified with the Christian afterl...
Found on
http://en.wikipedia.org/wiki/Annwn

In British mythology, Annwn is the other world.
Found on
http://www.probertencyclopaedia.com/browse/D3.HTM
No exact match found.