The Museo dell'Opera del Duomo - Siena Opera della Metropolitana - is one of the oldest private museums in Italy; located next to the Cathedral of Santa Maria Assunta, is located in that part called "New Cathedral". This building was part of the fourteenth-century project to expand the existing Cathedral, to celebrate the Sienese wealth in banking and to show its power, although the works were stopped due to the plague of 1348. The museum was established in 1869 with the approval of the Ministry of Education.
Among the sculptures placed in the rooms on the ground floor, there are the figures sculpted by Giovanni Pisano, which were placed on the facade of the Cathedral. The original grandiose thirteenth-century stained glass window created for the apse of the Cathedral and designed by Duccio di Buoninsegna has been located at end of the entrance hall, since 2004. On the first floor of the museum, there is another of his works created for the cathedral, the Maestà: this large panel was started in 1308 and finished in 1311. In the room, there is also a Nativity of the Virgin painted in 1342 by Pietro Lorenzetti and the Madonna with Child, a work painted by Duccio di Buoninsegna in his youth. In the two adjoining rooms, there are wooden sculptures depicting the Madonna with Child and the saints by Jacopo della Quercia. In the Sala del Tesoro (Hall of Treasure) there are about two hundred pieces of goldsmithery, including the Reliquary of San Galgano, one of the most important works of Sienese and international goldsmith's art, dated 1270 and from the Abbey of San Galgano.
On the upper floor, there is the Madonna with big eyes, a tempera and gold painting on wood by the Maestro di Tressa, in front of which the people of Siena made a vow before the Battle of Montaperti, that was fought against the city of Florence on 4 September, 1260. The title of the work is not due to the design of the Virgin Mary's eyes, but due to the rounded votive offerings that were situated around her. The work is considered one the oldest pictures painted in Siena. The room is enriched by a small crucifix, attributed to Giovanni Pisano and dating back to 1280. Also, in this room, there are the two Preachings of San Bernardino painted by Sano di Pietro in the fifteenth century. The so-called Sala degli Alfieri or dei Conversali contains works from various eras, including two altarpieces painted by Matteo di Giovanni, a Saint Paul on the throne dated 1516 by Domenico Beccafumi and two paintings by Luca Giordano.
From this room, going up two flights of spiral staircase, you enter the "Facciatone" (Facade), a name that continues to remind us of the project to expand the Cathedral.
Since 1996, the exit from the Museo dell'Opera di Siena has been by crossing through the church of San Niccolò in Sasso, which contains some of the works of the greatest Sienese painters of the seventeenth century.