If you are visiting Naples (as we did) then it is a must that you also visit the remains of Pompeii (as we did). Actually, if you have never heard of Pompeii then maybe don't bother, as you are probably (and I don't want to get judgemental here) going to get bored trudging around the excavations of a two thousand year old Roman city. There is only one pizza restaurant on-site and the shopping isn't very good unless you want to buy, say, a plastic reproduction centurion sword and helmet. For anyone else with even a passing interest in life in Ancient Rome, then go and visit; you won't regret it!
Getting to the Pompeii site is relatively easy. We took a train on the Circumvesuviana line that runs between Naples and Sorrento every thirty minutes. Here is a tip though, catch the train at Napoli Porta Nolana where the train starts, rather than the central Garibaldi station. This train gets very busy with local poeple as well as tourists, and most get on at Napoli Stazione Centrale.
Also, by the way, watch out for pick-pockets; I very nearly had my e-reader stolen from my rucksack. If I hadn't of felt the pocket zip starting to open behind me ... (on the other hand, if you do want to pick up a cheap i-Pod or tablet PC - no packaging or power-pack or questions asked - then there are plenty of people hanging around Napoli Stazione Centrale who will be happy to oblige).
The train journey from Porta Nolana to Pompei Scava Villa Misteri takes either 24 minutes or 37 minutes depending on whether you get the train that stops at all the stations on the line. Check out the timetable here. I wouldn't say it is one of the most scenic train journeys in the world, though Michael Portillo did take it on an episode of the BBC TV programme 'Great Continental Railway Journeys'. It does raise the anticipation levels watching Mount Vesuvius gradually loom into sight, though.
The walk from the Villa Misteri station up to the entrance of the archaeological site is about five minutes, though you might want to grab a glass of readily-available freshly-squeezed orange juice from outside the station before you go in. Whether you get an audio-guide from the entrance (and note, this is the only way to get a printed map of the site) is up to you, but there is lots of information out there on the net, e.g. this pdf of the site.
We visited Pompeii on a rather dull and wet day in December. The down-side to this is of course that your souvenir photos of the experience might not be very sunny (see below!), but the plus-side is that apart from near the Forum and the well-trudged sights on the tour-guide trail, we very much had most of the streets and buildings to ourselves. Pompeii gets around 2.5 million visitors a year, so I imagine that it could be a neck-craning and shoving match at the height of Summer.
Here then are some of my own souvenir shots of the day. I am not appending any explanation of what they depict. Not because I am lazy or can't be bothered to cut-and-paste from Wikipedia, but because I think the delicious mystery of these kinds of places is best left to the imagination to conjure up what could have been going on here on that fateful day in 79AD. (If you don't agree, then in the words of the immortal Frankie Howerd: Oh please yourself!)