The civic museum inside the Palazzo Pubblico, which alone justifies a visit to Siena. The route runs through the great state rooms of the Republic, including:
- The Sala del Mappamondo with Simone Martini's Maestà (1315) and the disputed equestrian portrait of Guidoriccio da Fogliano
- The Sala dei Nove with Ambrogio Lorenzetti's Allegory and Effects of Good and Bad Government — the most important surviving secular fresco cycle of the Middle Ages
- The Cappella del Consiglio with Taddeo di Bartolo's frescoes
A combined ticket includes the Torre del Mangia.