Solo, St Mark's Campanile works.
An elevator (no stairs) lifts you to the top of the reconstructed campanile for the definitive panorama — the whole city's terracotta rooftops, the lagoon, and the Alps on a clear day. The catch: it's a long, slow queue for a short slot at the top, the rebuilt-1912 tower has no historic interior, and the view from the cheaper San Giorgio Maggiore campanile is arguably better because it includes St Mark's itself.