Ouvrage L'Agaisen, Military museum in Sospel, France.

Ouvrage L'Agaisen is a military fortress located at 750 meters altitude in the Alps with four main blocks connected by underground tunnels. The site contains artillery and infantry installations, along with various chambers for combat, storage, and command functions that visitors can explore today.

Built between November 1930 and December 1934 by contractors Marting and Roussel at a cost of 24.6 million francs, the ouvrage was equipped from 1935 to 1937. In June 1940 its Block 3 75 mm turret fired some 1,800 rounds at Italian troops. Germans sabotaged the installations in October 1944, and American forces restored and used the position.

The fort's name comes from the Mont Agaisen where it stands. Volunteers have maintained it since 1992, and it opened for visits as a military museum. An instruction casemate let soldiers practise attack and defence, and the 75 mm turret of Block 3 is the feature visitors most often ask about.

The fortress sits on a mountainside and is reached by foot via a hiking trail starting from Sospel. Visitors should bring sturdy footwear since the climb is steep and requires good balance.

The fortress is equipped with specialized gas filtration systems designed to protect soldiers from chemical attacks. This technology was a key feature of the defensive design from that era.