San Gennaro’s head is in the duomo, but the rest of him is in his namesake two-story underground cemetery, used from the 2nd through 11th centuries. Some of the city’s earliest frescoes (those from Pompeii aside) are here, including one depicting a haloed San Gennaro with Mt. Vesuvius on his shoulders. Even earlier are a charming 2nd-century scene with Adam and Eve and a portrait of a family, with figures of each of the three members added over the years when their times came. Guides (most speaking English) will lead you down the wide aisles past the frescoed burial niches and early basilicas carved from the tufa rock, providing fascinating insights into the city’s long past—with a special nod to Sant’Agrippino, a 3rd-century bishop once interred here and who is almost as popular among Neapolitans as San Gennaro.