Museo dell’Opera (museum of the cathedral’s pieces of art) was housed in the ancient building adjoining the Siena Cathedral in 1869. It is often called Opera del Duomo. The museum occupies several rooms of the right-hand nave.

At the museum there are stored the masterpieces of the Siena Cathedral, which have ever been created for its decoration, such as: the facade sculptures of Giovanni Pisano, «Madonna del Perdono» by Donatello, high relief of Jacopo Quercia and many pictures with medieval scenes.

Also, you must see «Maesta», the altarpiece by Duccio di Buoninsegna. The church of St. Nicholas, built in the style of late baroque, is within the museum.