The Green Knight was filmed in Ireland.
Cahir Castle
In movie
Scene where Sir Gaywan is on a quest.
Real
Scene was shot Cahir Castle one of the largest castles in Ireland. They start building in 1142. That was done by Conor O'Brien, Prince of Thomond. The castle is located on an earlier fortification known as a cathair, which means stone fort. That’s where the name comes from. The castle is very well preserved.
Cahir