The cathedral contains some excellent artworks including frescoes in the Chapel of the Treasure of San Gennaro and some 4th-century mosaics. To one side of the Duomo is the 4th century Basilica Santa Restituta, the oldest chapel in Naples, containing columns believed to be from the Temple of Apollo. Under here is an interesting archaeological site tracing the Greek, Roman and early Christian city.
The nearest metro station is Piazza Cavour. Note that the archaeological area is open on weekdays with the same hours as the cathedral, but it is closed weekends and religious holidays.