We have toured in Italy with three different tandems, in fact bought our first one there 20 years ago. I agree with Dabbo that tandems don't really add to your experience of Italian cities. I'd never tandem in, into, or out of Naples, Rome or Milan. All these cities, plus Florence, Verona, etc have lovely small towns, villages and countryside ideal for cycling (though hot in summer) a few miles from their outer suburbs. For example, the area north of Verona airport, to the east of Lake Garda, is superb if you like hills.
We love Italy and go there at least twice a year. When we go in the summer we bring our tandem and stay away from big cities. When we go in autumn, winter or spring, we fly to Rome, Naples, Milan, Venice, etc and enjoy what cities have to offer. During those non-tandem holidays we sometimes rent bikes (eg we've done this in Lucca, Bergamo, Piacenza, Treviso, Verona, Rome, Padua, Pavia, Cremona, etc) cycle around the town and sometimes to outlying villas, eg in the hills to the north of Lucca). We have rented cars once or twice but more often take public transport to other cities and even villages. Nearly as much fun as tandeming. In the last 10 months we have tandem toured once in Tuscany/Umbria, once on the Slovenia/Italy border and next week are visiting Mantua, Parma, etc without our tandem. (Still too chilly for us.)