The dominant feature of the Diez townscape is the high medieval castle. The oldest parts of the structure date from the eleventh century. The castle was abandoned as a residence from the mid-1700s, and from 1743 to 1784, the count's castle was used as a Nassau office building. Subsequently, it served as a prison until 1927.
During World War II, Diez Castle was commandeered by the German Army to interrogate 'prisoners of special interest' captured on the western front, one prisoner being Gertrude Legendre, the female Office of Strategic Services clerk/translator captured in 1944. In the eighteenth and nineteenth centuries, the castle was the site of the largest processing center of Lahn marble.
Since June 2006 it has served as a youth hostel and, since 2007, also contains a museum.
References:The Château du Lude is one of the many great châteaux of the Loire Valley in France. Le Lude is the most northerly château of the Loire Valley and one of the last important historic castles in France, still inhabited by the same family for the last 260 years. The château is testimony to four centuries of French architecture, as a stronghold transformed into an elegant house during the Renaissance and the 18th century. The monument is located in the valley of Le Loir. Its gardens have evolved throughout the centuries.