This (12C-16C) castle, on top of a hill outside town, offers a splendid panorama of the Montagne Noire and the Pyrenees. The museum explains how woad is grown and the various stages involved in making blue dye, as well as the history of the ''princes of pastel'', merchants who became rich through trade and built magnificent palaces. On the 2nd floor is a dryer (18C) in which the woad ''cakes'' were placed, and photographs of the castle's restoration.