Complex sentence: The walls are decorated in trompe l'oeil by the Lombard Pietro Visconti, the images ore of an architectural nature, which create the large room is even more massive than it is.
Split into simpler sentences: The walls are decorated in trompe l'oeil by the Lombard Pietro Visconti. The images are of an architectural nature, which create the feeling that the large room is even more massive than it is.