The open top tourist buses run on three routes from Pazza Municipio. Naples is a very large city and this is a good way to get your bearings. I particularly recommend Line B, south-west along the bay, the quieter side of Naples, which provides great views of the bay and Vesuvius.
Piazza Municipio near Stazione Marittima
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But the tour buses are very expensive ... so use the local ones for about one euro you get 90 mins travel.
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