Citadelle Souterraine Lorraine

Comprising 7km of underground galleries, this cavernous subterranean citadel was designed by military engineer Sébastien Le Prestre de Vauban in the 17th century and completed in 1838. In 1916 it was turned into an impregnable command centre in which 10,000 poilus (French WWI soldiers) lived, waiting to be dispatched to the front. About 10% of the galleries have been converted into an audiovisual re-enactment of Verdun's WWI history. Half-hour, battery-powered-car tours, available in six languages, should be booked ahead.