Answer the following question: Château de Greifenstein -  The Château de Greifenstein is a ruined castle in the commune of Saverne in the Bas-Rhin département of France. Property of the state it has been listed since 1898 as a monument historique by the French Ministry of Culture. Given a choice of categories company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work, the text refers to which one?
Answer:
Building