Similar to the adjacent Hall of Columns in its spatial imposition and structural decorations, this small room called Antechamber/Foyer contains significant examples of architectural frescoes. The dramatic contents start with two Doric columns topped by high frieze arranged in two ways, a lower flap and floral swirls on the top.

Each column supports a decorated corbel with lion heads, frames and a series of mirrors painted with landscapes. In fact, the painted landscape is just one but it unravels on the entire hall, framed and interrupted by columns as if it were a sequence of wide mirrors opened to the outside. This landscape is characterized by the presence of castles, forests, small villages and a vast lake all set against the backdrop of a cloudy sky, where different types of birds take flight. According to some historians, the entire composition would be referring to the fiefdoms owned by the Borromeo family on Lake Maggiore. But the landscape references are too generic to confirm this iconographic hypothesis, though they should explain the presence of the emblem of the Arese family, on the date of the completion of the fresco, placed on a panel above.
As to the signature on the paintings, critics suggest distinguishing two different painters, one for the architectural composition and the other for the landscape depiction. It is in fact probable that like most of the compositions on the main floor, the architectural ones were by the Milanese painter, Giovanni Ghisolfi (1623-1683), who studied at an early age in Rome. He must have been helped by numerous painters, and among them were probably some exponents of the famous quadratura dynasty of Lombardy, the Mariani, active in other sites belonging to the branch of the Bartolomeo Arese family. The large landscape painting attests to a typical taste for ruins and is characterized by certain realistic precision, as their function remain undefined in the symbolic-allegorical level.