Although not often counted among culturally influential Italian cities like Venice and Rome, Naples benefits from access to the well-preserved artifacts of the ancient communities of Pompeii and Herculaneum, making the Naples Archaeological Museum one of the most significant exhibitions of Greek and Roman artifacts in the world. In short, there are many pieces of ancient architecture, including numerous frescoes and mosaics and even simulations of cities that once existed in antiquity. There's also quite an Egyptian collection that even includes typical mummy remains.
Most interesting to adult visitors may be the "secret cabinet", where those 11 and up can view sex-related objects up two a couple of thousand years old that have been the subject of various levels of censorship over the few hundred years the collection has been in existence. Imagine someone emptying your underwear drawer out and displaying it for people 2,000 years from now. Yeah, it's that interesting.
Note:Located at Piazza Museo 19. Cost for adult entrance is about $10 USD.