The Château de Castelnaud sits on a rocky outcrop on the south bank of the Dordogne, about 10 kilometres southwest of Sarlat, and is one of the best-preserved military fortresses in France. The English held it during most of the Hundred Years War, giving it a continuous adversarial relationship with French-held Beynac across the river.
The museum of medieval warfare inside is genuinely good — well-labelled (with English) collections of armour, trebuchets, siege equipment, and weapons, explained in context rather than just displayed behind glass. Working siege machine demonstrations take place in summer. The views from the walls down to the Dordogne and across to Beynac are among the best in the valley.