A magic artifact desired by Arthur and sought by Gawaine in a Dutch romance.
It was owned by King Wonder, who would only relinquish it if Gawaine brought him the Sword with Two Rings. This sent Gawaine on a long series of interlocking quests, culiminating in his return to Wonder’s court with the sword. Wonder completed the trade, and Gawaine returned to Arthur’s court with the Floating Chessboard.
Source
Roman van Walewein | Penninc and Pieter Vostaert, mid to late 13th century