Lyonesse is a legendary lost land often associated with the Arthurian legends. It is said to have been located off the coast of Cornwall, England, and is described as a beautiful and prosperous kingdom that sank beneath the waves due to a catastrophic event. The story of Lyonesse has inspired various works of literature and art, symbolizing the idea of lost civilizations. Some believe it may have been based on real places that were submerged due to rising sea levels or natural disasters, while others view it purely as a mythological tale.