Not to be confused with the Château de Castelnaud, Castelnau-Bretenoux was constructed in the 12th century and saw heavy action during the Hundred Years War, before being redeveloped in the Middle Ages for newer forms of artillery. It is beautifully (and strategically) set on a promontory above the broad valley. Much of the fortress is in ruins, but you can climb the 15th-century artillery tower , which has great views, and visit 17th- and 18th-century residential rooms (by guided tour).
Castelnau-Bretenoux fell into disrepair in the 19th century and was refurbished around the turn of the 20th century by Parisian opera singer Jean Mouliérat.
It’s about 11km south of Beaulieu-sur-Dordogne off the D940.
