hugo7: There is so much stuff to see in and around Napoli that it would be a shame to cut it out of your trip. Apart from the bigger draws of Herculaneum and Pompeii, what I'd be most interested in would be the Campi Flegrei, to the west and north-west of Naples, and the area north of the peninsula. This small area has a fascinating archaeological history. The Lago d'Averno is where Agrippa built a large fleet against Pompeius, and there is (what is often considered) the world's first road tunnel connecting the lake to Cumae (modern-day Cuma), the Grotta di Cocceio. (This is what I'd most like to see, but sadly it's not accessible to the public. It was used to store ammunition in World War II and some of that exploded and damaged the tunnel.) There's also a lot of fascinating history around Baiae and Miseno.
hugo7: There is so much stuff to see in and around Napoli that it would be a shame to cut it out of your trip. Apart from the bigger draws of Herculaneum and Pompeii, what I'd be most interested in would be the Campi Flegrei, to the west and north-west of Naples, and the area north of the peninsula. This small area has a fascinating archaeological history. The Lago d'Averno is where Agrippa built a large fleet against Pompeius, and there is (what is often considered) the world's first road tunnel connecting the lake to Cumae (modern-day Cuma), the Grotta di Cocceio. (This is what I'd most like to see, but sadly it's not accessible to the public. It was used to store ammunition in World War II and some of that exploded and damaged the tunnel.) There's also a lot of fascinating history around Baiae and Miseno.