For romance, Teatro La Fenice delivers.
One of Italy's great opera houses, an explosion of gold and blue rebuilt faithfully after its 1996 arson, where you can either take a daytime audioguide tour or — far better — see an opera in the very theatre that premiered Verdi and Rossini. The catch: the daytime tour is a quick look at an empty auditorium for the price; the magic really requires a (pricey, dress-up) performance ticket.