The Château de Joyeuse Garde is the site of a castle associated with Joyous Gard from Arthurian legend. Its ruins in the town of La Forest-Landerneau in Brittany date to the 6th century. It was listed as a monument historique on 6 October 1975.
The castle is the subject of "Joyeuse Garde", an 1859 poem by Algernon Charles Swinburne.
Wikipedia https://en.wikipedia.org/wiki/Château_de_Joyeuse_Garde
Address 6 Place du Château, La Forest-Landerneau 29800, France
Coordinates 48°25'26.829" N -4°18'56.785" E