This gallery is an elegant glass-and-iron covered passage following a Greek cross shape, with each of its four arms opening onto a street on one end and meeting at a rotunda, covered with a cupola, on the other. Built at the end of the 19th century -- 20 years after its larger Milanese counterpart -- this is a splendid Liberty-style (Italian Art Nouveau) construction with obvious Parisian inspiration. Inside, the galleria is lined with elegant shops and cafes.
You'll find a second Liberty-era gallery in town, Galleria del Principe di Napoli (off Piazza Cavour to the right; Metro: Piazza Cavour), which is virtually unknown, probably because of its location outside the most touristy area of Via Toledo.