These bunkers belonged to a system of fortifications built between 1575 and 1825. A large part of the surface works have disappeared but the bunkers remain and the galleries extend over around 10 km. You can visit a part of them, including the Bastion Waldeck with its domed vaults, powder arsenals and listening posts served by many corridors and staircases. Near to the walls stands a small bronze statue of d'Artagnan.