You can save money by buying a combination ticket to see Siena's top sites, near each other in the historic center. You don't have to do everything on the same day either, passes are valid for three days.
Siena Cathedral Combo Pass
The Cathedral pass is good for three days and includes skip-the-line-entry for six separate sites (one entry per site) connected with the magnificent duomo complex: the cathedral itself including the Piccolimini Library, the Crypt with its beautiful frescoes, Saint John's Baptistery, Museo dell'Opera (the museum of the cathedral), Facciatone with its panoramic terrace, and the Oratory of San Bernardino. The pass also includes the chance to see the stunning marble mosaic pavement if you visit during the weeks the floor is uncovered (in 2012, August 18 through October 24), although the cost is higher during this period.
Siena Cathedral Combo Pass can be bought in Siena (called the Opa Si Pass) or purchased in advance (no waiting in line, pay in US dollars) through Select Italy (information and booking).
Tower and Civic Museum Combination Ticket
You can climb Siena's tower for spectacular views of Siena and the surrounding countryside, but it's a steep climb and not recommended for those with claustrophobia, heart problems, or other physical ailments. The tower opens at 10:00 and closes at 3:15 in winter or 6:15 in summer. The combination ticket also includes admission to the nearby Civic Museum and is for sale at the ticket booth for the tower.
Visiting Siena in Summer
Tip: Spend the night and enjoy Siena in the evening when it's not so crowded. Most tourists come only for the day but the town in the evening is really beautiful and worth an overnight stay. If you're going during the Palio Festivals, be sure to book well in advance. For places to stay, see Top Rated Siena Hotels.