Although Naples itself is worth the visit, this is where we took a trip to Pompeii, which is a fascinating journey into the history of the inhabitants of this place at the time of the eruption of Vesuvius in 79 AD. Although we had been before, they are continuing to excavate the site and more buildings are being unearthed. I would recommend this trip to anyone who is not wheelchair bound, as I can't see a chair getting around the various levels. Another caution is that it does get exceedingly hot, so water is essential and a fan is really helpful.
It is also possible to visit Herculaneum from this port, which we have done in the past and this is also worth a visit. In some ways it is better preserved than Pompeii, but I rate them equally as being worth a visit.
There are internet cafes in the city centre, another opportunity for a great cup of coffee.