Housed in the Renaissance-era Palazzo Piccolomini, Siena's State Archive isn't a usual stop on the standard tourist itinerary, but it provides ample reward for those who choose to visit. The small on-site museum takes its name from the pride of the archive's collection: 103 small late-13th-century painted and gilded wooden panels known as the 'Tavolette di Biccherna'. Created as covers for the municipal accounts books, the biccherne were painted by Sienese artists including Ambogio Lorenzetti and Taddeo di Bartolo.
These and other evocative, historically significant documents (many medieval) can be seen on daily guided tours (in Italian only) – non-Italian speakers are welcome to browse the exhibits while the tour is underway. You'll want to linger in front of the cabinets containing the biccherne, enjoying their scenes of Sienese life between the 13th and early 18th centuries and marvelling at the skill of their artists. Ensure that you also view the illuminated Constitution of Siena (c 1310), which was written in Italian rather than Latin – very unusual for the time. There are also historical documents about the city's contrade (districts) and the Palio, including drawings of costumes and processional floats.
Guided tours in Italian, English and French can be arranged by emailing as-si.comunicazione@beniculturali.it. To find the museum's entrance, head to the back left of the courtyard and take the stairs to the 4th floor.