The shelter gallery runs for about 180 meters along a parallel axis equidistant from Viale Merello and Viale Sant’Ignazio. The main entrance was located on Don Bosco Street, although there were a number of corridors transverse to the main axis that also allowed access to the shelter from other entrances located in private courtyards on nearby streets. The tunnel did not originate as a wartime shelter during World War II, but was part of an articulated series of still-existing underground routes, with similar dimensions and excavation characteristics, that are distributed along the entire northern side of the city, from the ramparts of Buoncammino to the market area of Via Pola; these were probably built in the 1700s by the Piedmontese outside the walls for military purposes, as escape routes or counter tunnels.
Much of this pre-existing network of tunnels was quickly repurposed at the beginning of World War II as a shelter for the civilian population. At the end of the war the tunnel was forgotten, and the various entrances, including the main one on Don Bosco Street, walled up, allowing it to reach the present day almost intact.
