In La Tavola Ritonda, an island where Tristan and Isolde washed up on their way to Ireland from Cornwall. The Castle of Tears, owned by the parents of Lord Galehaut, stood on the island, and Tristan had to conquer it in order to leave the island.
In the Prose Tristan, it is called the Giant’s Isle. The “Wicked Custom” was that the visiting knight’s lady would be compared to the paramour of the island’s lord. Whichever was least beautiful was beheaded.
La Tavola Ritonda | 1325-1350
Prose Tristan | 1230-1240