Austro-Hungarian authorities, immediately prior to the First World War and during the War, began the construction of an underground tunnel system with communication passageways under the city’s hills to shelter the city’s population and to serve as ammunition stores. Not a single hill in the inner city was spared from drilling and digging.
A widely spread network of underground tunnels/shelters was created. Under the central city hill Kastel, there are two shelter tunnels, one is directly underneath the fort located on the top of the hill, and the second one is at the foot of the hill. This tunnel is about 400 metres long.