Annwn

From the Brythonic an (“abyss”) and dwfn (“world”), known throughout Celtic
myth as “Land Under Wave,” or the “Revolving Castle” (Caer Sidi); formerly a
fortified island of great natural beauty with freshwater streams and a circularshaped
city, at the center of which was a magic cauldron of immortality. These
details clearly point to Atlantis, while Annwn’s cauldron is a pre-Christian reference
to the Holy Grail—another legendary link with the sunken civilization.