A network of military tunnels excavated during and after World War II, running beneath the hills north of the old German quarter. The tunnels were expanded during the Cold War and form an unexpectedly extensive underground complex. Parts of the system are open to visitors as a heritage site.
The contrast between the German-built streets above and the concrete bunkers below underlines how many layers of occupation and conflict this city has absorbed. The tunnels are cool in summer and make a good break from the heat. Tours go about 400 metres into the system, with displays of military equipment and photographs documenting the construction. Some sections have been converted to wine storage and are used commercially.