The Drowned Island of Ys (Breton)
King Gradlon's daughter Dahut persuades him to
grant her the city of Ys. She takes a new lover every night and subsequently
has him killed. Finally a demonic lover outwits her and persuades her
to obtain from her father the key to the dyke that has protected Ys
from the sea. Her lover opens the gates and the city is drowned. Gradlon
escapes, but only by following the instructions of St Guénolé
and casting Dahut from his horse.