premise: The most important are clustered around three adjoining the triangular Piazza della Ceterna named after the city's 13th-century travertine well, surrounded by elegant palaces; the Piazza del Duomo, grouping church and town hall as the center of civic and religious power; and the Piazza delle Erbe ?­market place with twin Salvucci towers.
hypothesis: The Salvucci towers are open to visitors.