Underground Citadel of Verdun
The Citadel of Verdun was first constructed in the early 17th century on the site of the Saint Vanne abbey in the center of the city, and later expanded upon by the famous French Military engineer Sebastion Vauban. At the end of the Franco-Prussian war it was the last citadel to surrender to Prussian forces, and in the following years was significantly extended and improved with 40 km of underground tunnels. During the Battle of Verdun, the citadel served as a headquarters and hospital for the French divison stationed in the region. It is now a museum dedicated to teaching the public about the battle.