Lyonesse

Lyonesse is a country in Arthurian legend, particularly in the story of Tristan and Iseult. Said to border Cornwall, it is most notable as the home of the hero Tristan, whose father was king. In later traditions Lyonesse is said to have sunk beneath the waves some time after the Tristan stories take place, making it similar to Ys and other lost lands in medieval Celtic tales, and perhaps connecting it with the Isles of Scilly.

Read more about Lyonesse:  Lyonesse in Arthurian Legend, Analogues in Celtic Mythology, Lyonesse in Modern English Literature, Other Uses of Lyonesse