Traverse five centuries along Naples’ Bourbon Tunnel. Conceived by Ferdinand II in 1853 to link the Palazzo Reale to the barracks and the sea, the never-completed escape route is part of the 17th-century Carmignano Aqueduct system, itself incorporating 16th-century cisterns. The standard tour does not require prebooking, though the Adventure Tour (85 minutes; adult/reduced €15/10) and adults-only Speleo Light Tour (90 minutes; €15) do.
The Via delle Memorie Tour (60 minutes; adult/reduced €10/5) is only available in English for groups; see the website for details. Note that there are two other entrances to the Galleria Borbonica: one at Via Domenico Morelli 61 and the other at Via Monte di Dio 14.