On the outskirts of Napels, and easily reached with the local train is Herculaneum. Much smaller but an alternative to Pompeii. The well-to-do Roman coastal town was destroyed by the same eruption of Vesuvius in AD79 which destroyed the larger Pompeii. Partly lying under the modern Naples suburb of Ercolano, the site of Herculaneum hasn't been fully uncovered and is much smaller and more manageable to visit than Pompeii. Destroyed in a different way, by a pyroclastic surge which killed inhabitants, carbonised wood and left the city buried under 16-25 metres of rock, the archaeological site offers a different kind of insight into the Roman world.
The new town is built just above and the views of Vesuvius are ever present as you walk around this fascinating site.