Pompeii is one of the top Roman era attractions in Italy. It's also pretty easy to get to. The main train line, the FS from Naples, and the private line, the circumvesuviana, both arrive in the modern Pompei, albeit at different stations, as you see on our Pompeii map.
As you can see from the map, the ancient town of Pompeii is not so much smaller than the modern town that's grown up around it. You can take quite a long time exploring it--the whole city is at your feet.
And it takes a while. The ancient streets and sidewalks aren't exactly flat. It'll tire you out sooner than you think. There is a cafe inside, so you can have a break, but it's still an amazingly complex site.
It used to be said that the modern town, differentiated from the older one by its spelling--Pompei, with one "i"--wasn't worth staying in. But it's a pleasant enough town, especially if you stay in one of our recommended hotels, chosen for their quiet locations. Remember that lots of folks do Pompeii on a day trip, so nights can be nicely quiet and relaxing. Pompeii, in fact, has a nice passiagiata, an evening stroll that citizens participate in, walking up and down the main street, Via Plinio, that marks the southern boundary of the ancient Pompeii excavations.
And, you can now tour Pompeii at night, with Le Lune di Pompeii (you can book a ticket online through the link).
Pompeii Attractions
The recommended things to see in Pompeii are marked on our map.
Ancient Pompeii is your main target here. You'll see villas, Roman baths, the forum, and the city of Pompeii. Don't skimp on the time you spend here. Before you go, you might want to check the event page.
Santuario di Pompei is the main church of Pompei and gives its name to the stop on the Circumvesuvius stop on the train from Naples. There is a small museum downstairs. It has quite a stunning facade, and marks the spiritual center of the new Pompei.
La Bettola del Gusto Ristorante on Via Sacra across from the FS station offers good food at reasonable prices. It's especially convenient if you're staying at the Hotel Diana, which doesn't have a restaurant of its own.

Pompeii - Where to Stay
Hotel Diana Pompei a reasonably priced three star hotel in a quiet area near the FS station with good internet connection and helpful staff. Highly rated by folks who've stayed there. Nice public areas.
Hotel Visagi is a highly rated hotel 800 meters from the excavations, also a three star hotel. Reasonable.
If you're in Rome, The Context Travel Pompeii Excursion would put you and your family in the hands of experts. The Select Italy Amalfi Coast & Pompeii - Private Chauffeured Road Trip would give you a lot to see in a very full day.
Pompeii, and to some extent its sister site Herculaneum, are notable for being destroyed by a particularly ferocious eruption of Vesuvius. Time stopped at that very moment. The archaeological site became a vast museum of that moment in time, which is why it is so compelling.