At the height of its power and influence, Luxembourg was protected by three rings of defense comprising 53 forts and strongholds. During the many phases of the fortress's construction, the rock itself was hollowed out to form a honeycomb of passages running for nearly 24 km (15 mi) below the town. Ten gates controlled admittance through the walls, and the town was, in effect, 440 acres of solid fort. The Casemates served not only defensive purposes but were also used for
storage and as a place of refuge when the city was under attack. Two sections of the passages, containing former barracks, cavernous slaughterhouses, bakeries, and a deep well, are open to the public.
Pl. de la Constitution, Luxembourg City, Luxembourg