The Museum of the Opera del Duomo opened in 1967 and was then expanded to display paintings, sculptures, sacred furnishings from the entire diocese, in a suggestive path under the presbytery of the Cathedral and around the Romanesque cloister. From the arch below the bell tower of the Cathedral you enter the "vaults" of the Museum. This large basement was used for centuries for burials, and for this reason it preserves coats of arms and frescoes of the most important families from Prato. From the "vaults" you enter the Chapel of S. Stefano, entirely frescoed by the Miniati brothers around 1420. A corridor leads to the Romanesque Cloister of the Cathedral (circa 1170), in white marble and green serpentine, with refined zoomorphic capitals and inlays; From here you can access the seventeenth-century Hall with works by Matteo Rosselli, Empoli, Mehus, and a remarkable altarpiece with the Guardian Angel (1675) by Carlo Dolci. From the next Hall of the sixteenth century you reach the Hall of the Pulpit, which has in the center the original marble parapet (1434-38) of the Pulpit by Donatello and Michelozzo, in which a joyful dance of putti, from the complex perspectives glimpses. The very refined bronze capital originally placed at the base of the pulpit is also by the same artists. The Capsella (1446) by Maso di Bartolomeo, which contained the relic of the Sacra Cintola, is a precious Renaissance jewel. Also remarkable are two glazed majolicas by Andrea della Robbia. In the adjacent Hall of the fifteenth century are exhibited paintings, including the Funeral of Saint Jerome (1453 ca.), masterpiece by Filippo Lippi, a poignant Crucifix on shaped table of Botticelli, and a detached fresco by Paolo Uccello, with Blessed Iacopone da Todi. 
Continue through a basement area, where the excavation has brought to light finds from the Etruscan period to the fifteenth century, and from here you go up in the room dedicated to the Sacred Belt of the Madonna, the most valuable relic of the territory, where are exhibited among other things some suggestive marble reliefs (1358-60) by Niccolò del Mercia from Siena. The next room houses the precious Parato di Santo Stefano (1590 ca.). The last room preserves panels of polyptychs from the 14th-early 15th century, remarkable sculptures, including a head of Crucifix from 1230-40 and a relief by Giroldo da Como, from 1262.
The visit includes also access to the transept of the Cathedral of Santo Stefano with its frescoed chapels. Among the five chapels the most worthy of note are: The Major Chapel, the most famous, preserves one of the most important fresco cycles of the Renaissance, with the stories of Santo Stefano and San Giovanni Battista (1452-65) by Filippo Lippi; on the side, the Chapel of the Assumption frescoed in 1433-34 by Paolo Uccello, with stories of the Virgin and Santo Stefano; next to it is the Capella Vinaccesi which preserves frescoes by Alessandro Franchi (1873-1876).