I'm now listening to Joanna Newsom's "Ys". In an interview with Uncut, Joanna said Ys is a reference to a city island in Breton mythology that was built below sea level and had a wall around it. Then the dam got breached and the city flooded. Several myths surrounded this, but the one Joanna has heard involves the king's daughter, who was a hedonist, and the city declined into a state of self-gratification, greed and laziness.

"The king's daughter would take a new lover every night and put a mask on him. It was a magical mask, so after she was finished with him, these large prongs would come out on the inside of the mask and kill him, and then she'd throw him into the ocean. Then one night she had a visitor who was the devil, or in other versions was this righteous figure who would punish her for her ways. She couldn't put the mask on him because she fell in love with the beauty of his face. He convinced her to go and take her father's keys. She did so in a trance, unlocked the wall and the sea rushed in."