The exterior features a Renaissance portal which leads to a single nave with a barrel vault that supports the two upper rooms, where the grain stockpiles were located.
The oratory was the seat of two confraternities, whose contemporary presence is testified by the altarpiece, decorated by a double-faced canvas, which can be rotated by means of a mechanism placed at the back: on one side is depicted The Apparition of the Blessed Sacrament to the brothers, on the other The Assumption of the Virgin, with the patron saint of the castle, St.Onofrio, portrayed on the left.
The display of one side or the other indicated which of the two brotherhoods was using the oratory at that time..
