The Diocesan Museum of Sacred Art, with the adjacent Oratory of San Bernardino, is a place with a magical and suspended atmosphere in which to reread in one breath the history of the spirituality of the territory and Sienese painting from the thirteenth to the eighteenth century.

The architectural structure of the Oratory of San Beranrdino, of late medieval origin, was renovated during the sixteenth century. Born to house the Confraternity of Santa Maria and San Francesco, in the 16th century the Oratory was named after the friar Bernardino Albizzeschi, who was already highly venerated in his life and canonized in 1450 just six years after his death, famous for his fervent sermons in the Sienese squares. On the sober brick facade stand out the elegant travertine portal and the symbol of San Bernardino, which also recurs on the Palazzo Pubblico and the Duomo: a radiant sun in the center of which the letters JHS, abbreviation of "Jesus hominum salvator" (Jesus savior of men).

The ceiling of the entrance hall, with the Madonna protecting Siena, San Bernardino and Santa Caterina by Arcangelo Salimbeni and Francesco Vanni, is surrounded by lunettes dedicated to the life of San Bernardino, whose construction was carried out by Ventura Salimbeni, Rutilio Manetti and many others artists of the first half of the seventeenth century. Inside the museum you can admire paintings and sculptures ranging from the thirteenth to the seventeenth century and numerous goldsmith objects. The heart of the museum remains the splendid chapel of the upper oratory, dedicated to Santa Maria degli Angeli, with a coffered ceiling with cherub heads on a blue background. The walls are entirely frescoed with the Stories of the Virgin, offering a unique example of Sienese painting of the early sixteenth century represented here by its protagonists: Domenico Beccafumi, Giovanni Antonio Bazzi known as “Sodoma” and Girolamo del Pacchia.