Commonly called "castle", it is in fact a vast Cistercian monastery; founded in 1234, it was one of the richest in the region, also known as the Gorizia monastery. It was a victim of the reformist agenda of Emperor Joseph II and closed in the late 18C. Its crypt contains the tomb of King Charles X of France, who died in exile. Rebuilt after the Second World War, it still has an impressive arcaded courtyard.