I've just been on a guided tour of the metro excavations in Naples's Piazza Municipio. Visits are possible Saturdays and Sundays for the rest of May, so if you are in the area and speak some Italian it is well worth booking.
Although there are limits to how close you can get to the archaeology, due to the fact that this is a working construction site with all the hazards involved, the guides (all archaeologists working on the site) do an excellent job of explaining what can be seen and using site panels to show the inaccessible areas.
This is currently Italy's largest urban excavation and phases date from the Greek colonisation of the area through to the 1800s when the piazza was created. Of particular interest is the evidence for the Roman port - including the three boats that were found last year and which are currently being undergoing conservation interventions off-site. There is also a Roman bath building.
Later periods reveal the Anjou and Aragon phases of the nearby Maschio Angioino, including large sections (including towers) of its outer defensive system.
No photos are allowed to be taken during the visit, but this image gives an idea of the site (taken from the external walkway open to the public).
Many of the archaeological features will be incorporated into the metro station design and so on permanent display. This station will be the connection between the metro lines 1 and 6, so has a reasonable amount of space for exhibiting what was found. However, the works won't be finished until 2012 at the earliest, so if you have the time in the coming weekends, book a visit now:
Contact: CDP Relazioni Pubbliche
Phone: 081 764 6206 - 338 871 7644 (Mon to Fri between 10:30-13:00, 16:30-18:30)
Visits possible: 9:00-13:00 on 23, 24, 30, 31 May 2009