Whether you go for Giovanni Lanfranco's fresco in the Cappella di San Gennaro (Chapel of St Janarius), the 4th-century mosaics in the baptistry, or the thrice-annual miracle of San Gennaro, do not miss Naples' cathedral. Kick-started by Charles I of Anjou in 1272 and consecrated in 1315, it was largely destroyed in a 1456 earthquake, with copious nips and tucks over the subsequent centuries.
Among these is the gleaming neo-Gothic facade, only completed in 1905. Step inside and you'll immediately notice the central nave's gilded coffered ceiling, studded with late-mannerist art. The high sections of the nave and the transept are the work of baroque overachiever Luca Giordano.
Off the right side of the nave, the Cappella di San Gennaro (also known as the Chapel of the Treasury) was designed by Theatine priest and architect Francesco Grimaldi, and completed in 1646. The most sought-after artists of the period worked on the chapel, creating one of Naples' greatest baroque legacies. Highlights here include Jusepe de Ribera's gripping canvas St Gennaro Escaping the Furnace Unscathed and Giovanni Lanfranco's dizzying dome fresco. Hidden away in a strongbox behind the altar is a 14th-century silver bust in which sit the skull of San Gennaro and the two phials that hold his miraculously liquefying blood.
The next chapel eastwards contains an urn with the saint's bones and a cupboard full of femurs, tibias and fibulas. Below the high altar is the Cappella Carafa, a Renaissance chapel built to house yet more of the saint's remains.
Off the left aisle lies the 4th-century Basilica di Santa Restituta, the subject of an almost complete makeover after the earthquake of 1688. From it you can access the Battistero di San Giovanni in Fonte. Western Europe's oldest baptistry, it's encrusted with fragments of glittering 4th-century mosaics.
The Duomo's subterranean archaeological zone, which includes fascinating remains of Greek and Roman buildings and roads, remains closed indefinitely.