On the side overlooking the medieval part of town, 
inside the castle's high walls, is a spacious courtyard, with another building set perpendicular to the rear façade of the main building.
The final owners of the castle were the princes of the Brancaccio family who ultimately left in 1899.
Castello Brancaccio di San Gregorio
They added a tower, a large guest house and an arch joining the two buildings and leading down into the medieval town. As was the popular practice at that time, these additions and renovations
were designed in pseudo-medieval style. The ground-floor windows, for example, were replaced by Guelf-cross windows, and the chapel's old bell tower was turned into a turret.
Inside the rooms are decorated with a series of frescoes dating to the 16th century, attributed to Federico Zuccari (who then also worked on the Villa d'Este in Tivoli) and to the 18th century, attributed to the Neoclassical painter Andrea Appiani. In some rooms, the paintings shows the history of the Brancaccio family. Other rooms are decorated with grotesque motifs, and still others with landscapes. Some of the ceilings are frescoed with mythological scenes, including an Allegory of Sacred and Profane Love.
In 1989 the Brancaccio family left the castle to the municipality of San Gregorio da Sassola, as they had already done with Villa Brancaccio, which is now a public park.
