Piscina Mirabilis

Lonely Planet review

An archaeological pièce de résistance, the Piscina Mirabilis (Exquisite Pool) lies tucked away in a Bacoli backstreet. To access it, contact custodian Signora Filomena at No 9. Awaiting underground is the world's largest Roman cistern. Featuring 48 soaring pillars and a barrel-vaulted ceiling, it resembles a great subterranean cathedral, eerily bathed in shafts of sunlight.

Admission is free but save face and tip the Signora - around €1.00 will do.

Erected in the Augustan age, its 12,600 cubic-metre water supply served the military fleet at nearby Miseno. Fresh water flowed into the cistern from the Serino river aqueduct which was then raised up to the terrace with hydraulic engines, exiting through doors in the central nave. To this day, engineers marvel at the cistern's sophistication: its pounded terracotta walls and floor are still emulated today.