Naples is built on tunnels. Greeks quarried tufa stone to build Neapolis (470 BC) and left tunnels. Romans expanded them into aqueducts. Medieval Neapolitans used them as cisterns. WWII civilians sheltered in them during the 181 Allied bombing raids. The result: Naples has more underground space than any city in Europe — an estimated 2 million m² of cavities, tunnels, cisterns, catacombs, and chambers, most of them unmapped. These 5 experiences take you into the mapped parts — and they're enough to understand that the city above is just the surface layer of something much older, much deeper, and much more extraordinary. Rome underground →
Plan my underground Naples →1. Napoli Sotterranea (Piazza San Gaetano 68, €12, guided tours hourly in English). THE essential Naples underground experience. Descend 40 meters via a narrow staircase into Greek-Roman aqueduct tunnels. Walk through passages so narrow you squeeze sideways (claustrophobes: one section is genuinely tight — about 50cm wide for 10 meters). Emerge into a WWII bomb shelter (scratched walls, children's drawings, hospital beds still in place). Then: an underground garden lit by a hole in the street above — vegetables growing 40 meters below a parking lot. 1.5h guided tour. The most dramatic guided tour in Italy.
2. Galleria Borbonica (Bourbon Tunnel) (Vico del Grottone 4, entry from Via Morelli or Piazza del Plebiscito, €10-15 depending on route). Built 1853 as an escape tunnel for King Ferdinand II from the Royal Palace to the barracks. Never completed. Repurposed as WWII bomb shelter (20,000 people lived here during raids). Now: vintage cars and scooters from the 1950s-60s still parked underground (stored after the war, never retrieved — owners dead, forgot, or emigrated). Statues, building debris, and a 1943 ambulance. The "adventure" route involves wading through underground water and using a raft (€15). The standard route is dry (€10).
3. Catacombe di San Gennaro (Via Capodimonte 13, €9, guided tours every hour). The largest early Christian catacombs in southern Italy. Two levels: upper (2nd century) and lower (3rd-4th century). Frescoes, mosaics, carved tombs, the original burial of San Gennaro (Naples' patron saint, whose blood miraculously liquefies three times a year — the cathedral ceremony is the most intense religious event in Italy). The guided tour is run by a social cooperative from the Rione Sanità neighbourhood — young locals who've transformed catacombs tourism into community development. Supporting them = supporting the neighbourhood.
4. Cimitero delle Fontanelle (Fontanelle Ossuary) (Via Fontanelle 80, Sanità neighbourhood, free). A cave containing the bones of 40,000 people — plague victims, cholera victims, unnamed poor. Neapolitans developed the cult of pezzentelle: adopting a skull, cleaning it, placing it in a small shrine, praying for its soul in exchange for favours. The practice was banned by the Church in 1969 but the skulls remain in their shrines. Open, free, unsupervised. The most haunting space in Naples.
5. Complesso Monumentale di San Lorenzo Maggiore (Piazza San Gaetano, €9). Underground excavations beneath the medieval church reveal: a complete Roman market street (macellum — the ancient equivalent of a shopping mall, with shop counters, bakeries, and a treasury still visible at the original street level, 10 meters below the current street). You walk where Romans walked, at the height they walked. The medieval church above is also extraordinary — Boccaccio met Fiammetta here in 1334.