The casemates of the former Luxembourg Fortress, in the Old Town of the capital, stretch in the Bok rock for twenty kilometers at a depth of up to 40 meters. They were dug into the limestone rock in 1644 and continued in 1715, with exit windows to the surface, for better ventilation, from which in our time you can observe the gorge and the old quarters of the city. Visiting the underground passages has been open to tourists since 1933. The excursion program includes visiting the tunnels, the ruins of the fortress with artillery positions with cannons, the former prison cells of the casemate, the premises where the finds from the underground passages are presented.
During World War II, Luxembourg civilians waited out British air raids in the casemates. The two-storey bridge Pont du Château, over the road between the two parts of the Bok rock, is also an important part of the fortifications.