One of the most remarkable features of Luxembourg City is its medieval heritage, particularly evident in the old town. This central area, filled with wine bars, designer shops, and sunny public squares, was formerly part of an imposing fortress that was controlled by various dynasties over the centuries. At its height, the city was home to 40 fortifications, including forts, bastions, barracks, workshops, arsenals, storage facilities, and command centers, covering over one and a quarter square miles.
In 1644, during the period when Luxembourg was under the Spanish Netherlands, the first defensive tunnels were excavated into the Bock cliffs. However, the citadel was not completely secure; in 1684, the army of French King Louis XIV captured the region, prompting royal engineer Vauban to renovate its defenses. Following Luxembourg’s incorporation into the Austrian Empire in 1714, the military expanded the extensive underground network. By the end of this effort, the city had 23 kilometers of tunnels capable of housing soldiers. By the eighteenth century, the well-positioned citadel was encircled by three layers of fortifications, which led to its nickname, “Gibraltar of the North.”