Luxembourg’s Bock cliff, with its fortifications and cannon-loopholes, is where you’ll find the entrance to the famous Casemates (Casements du Bock), a 21-kilometer network of underground passages hewn from solid rock. Capable of sheltering thousands of defenders, as well as equipment, horses, workshops, kitchens, and slaughterhouses, the Casements – some of which date back to Spanish rule in 1644 – cover an impressive 40,000 square meters. Today, much of these remarkable fortifications can be explored on foot, while organized guided tours are available for those wanting to learn more about the tunnels’ fascinating history. On the Bock plateau itself are the remains of the old castle, discovered in 1963. There are beautiful views of the suburb of Grund and the Rham Plateau, the old 19th-century barracks, and the big towers and remains of the Wenceslas wall standing from 1390.