Naples has been digging since the Greeks (4th century BC). The tufa rock beneath the city is honeycombed with tunnels, cisterns, catacombs, and WWII air-raid shelters.
Plan this experience →Napoli Sotterranea (Piazza San Gaetano, €12/1.5h guided): the classic tour. Greek-Roman aqueduct, WWII shelter (graffiti still on walls), narrow passages (some require candles). The most dramatic underground experience in Italy. Galleria Borbonica (Via Morelli, €10–15): 19th-century escape tunnel for the king, full of WWII vehicles, cisterns. The "adventure route" involves rafting through flooded tunnels (€15). Catacombe di San Gennaro (Via Capodimonte, €9): early Christian frescoes, the tomb of Naples’ patron saint. Guided by the La Paranza cooperative (local youth who restored and manage the site — a remarkable social project).