Definitely one of the most unusual things to do in Naples is exploring the unfinished underground passage known as the Galleria Borbonica—the Bourbon Tunnel.

 It was begun in the 19th century, on the instructions of King Ferdinand II, as a way for him to escape from the Royal palace to the safety of the military barracks on what is now Via Morelli.

 It was never finished, but the carved tunnels were later used as an air raid shelter and emergency hospital during World War II.

Access to its huge galleries and spooky tunnels is by tour, during which you can see the cisterns and a variety of relics and debris from its various uses, including old cars, Vespas, motorcycles, and fragments of statuary and architectural detail.