The Grand Salon is dedicated mainly to chamber music concerts.
It is richly painted and decorated in light colours and dedicated to King Victor Amadeus II, who is portrayed on the west side surrounded by blue drapery.
The mythological allegories relate to philosophical thought. Beside the comet, the painted motto in the centre of the medallion on the keystone is "specchio son di virtù e guida". The Magi are represented at the top of the side walls in a movement converging to the comet painted on the arch's central medallion.
Above the French doors feature the allegories of the arts: Architecture, Painting, Mathematics and Astronomy.