Manoir de Pen Castel, Manor house in Le Croisic, France

The Manoir de Pen Castel is a former coastal battery building located on the Le Croisic peninsula at the boundary with Batz-sur-Mer near Valentin Beach. The structure was later converted into a private residence and sits directly along the coastal path connecting both towns.

The building was constructed in 1747 as a coastal defense structure to protect the bay. In 1836, the Janvier de La Motte family purchased the property and converted it into a vacation residence, incorporating the former guardhouse into the new structure.

The manor shows how French coastal fortifications were converted into private homes in the 19th century, reflecting a shift from military to social purposes. This transformation represents how strategic locations gained new roles in local life.

The manor stands at the end of Valentin Beach on the Pointe du Fort, on the coastal path linking Le Croisic and Batz-sur-Mer; the route passes the property and gives views of its seaward facade. The building itself is a private residence and is not open to visitors, so plan the walk as an exterior viewing only.

Henri Becquerel, who shared the 1903 Nobel Prize in Physics for the discovery of radioactivity, died at the manor in 1908 while staying with his father-in-law Edmond Lorieux, who had bought and enlarged the property in 1876. The death of a physicist known for work on uranium rays occurred in this coastal house rather than in a laboratory.