The presence of the supernatural is made explicit in the title of this picture. The reference is to the story of Branwen, daughter of Llŷr. (Shakespeare’s Lear?), in the Mabinogion. The linking of this story from the Mabinogion and what appears at first sight of a window with the sea beyond is typical of the way that DJ’s mind works: evoking associations.

Manawydan is an important character in the Second Branch of the Mabinogi, the Mabinogi of Brânwen, Daughter of Llŷr. In this tale, Manawydan serves as advisor to his brother Brân the Blessed, the King of Britain. He sits beside Brân at the feast celebrating the wedding of their sister Brânwen to Matholwch, king of Ireland, an occasion which is meant to solidify an alliance. When their half-brother Efnisien, upset that he has not been consulted, mutilates Matholwch's horses, Brân sends Manawydan to offer recompense. Later, when word gets back to Britain that Matholwch has been mistreating Brânwen, Manawydan joins Brân's rescue effort.

In the ensuing war, Manawydan is one of only seven men to survive. The mortally wounded Brân asks Manawydan and the others to cut off his head and take it back to Britain; it will continue speaking and keeping them company in the meantime. They come to a wondrous castle on the island of Gwales, where they enjoy a great feast and forget their sorrows. Manawydan recognises that opening the door of the castle “facing Cornwall” will break the spell, but one day his companion Heilyn son of Gwyn grows overcurious and opens it, and all their sorrows return. The group takes Brân's head to the White Hill (the loation of the Tower of London) and bury it there, where it serves as a talisman against foreign invasion. (Gwales, or Grassholm, is a small uninhabited island some 8 miles offshore from the southwest coast of Pembrokeshire.)