The rarified atmosphere of this place makes it an essential reference point for the history of sacred art of the territory. Paintings of the thirteenth and fourteenth-century artists can be admired, including the 'Maestro di Tressa', Bartolomeo Bulgarini, Luca di Tommè and Taddeo di Bartolo; there are also some frescoes from the church of S. Francesco by Pietro and Ambrogio Lorenzetti, to be noted in particular the beautiful 'Madonna del Latte'. Following these there are works of the sixteenth and seventeenth centuries: the 'Cristo Portacroce' by Beccafumi, small paintings by ‘Sodoma’ (Giovanni Antonio Bazzi) and Riccio and some works by Ventura Salimbeni and Bernardino Mei, as well as a collection of sculptures, including some by Domenico di Niccolò dei Cori and by Antonio Federighi, and numerous objects of goldsmith's art.
The heart of the museum is in the old rectangular room of the 'Oratorio Superiore' with its coffered ceiling and cherub-heads on a blue background. The walls are entirely frescoed with 'Le storie della Vergine' and offer a marvellous example of Sienese painting from the first part of the sixteenth century, represented here by its protagonists Girolamo del Pacchia, ‘Sodoma’ and Beccafumi.