It was built by Galeazzo II Visconti starting from 1360 and it ended in only five years. More than a military castle, it was a splendid and fine residence. This destination is underlined by the elegant terracotta windows with two and three lights and by the refined decorative taste of the courtyard. From the wide frescoed cycles with battles, hunting scenes and episodes of courtly life, painted to decorate rooms, porticoes and loggias, there are remaining significant tracks: in particular, the complete decoration of the Blue Room, with gold and lapis lazuli, maybe seat of the well-known Visconti library, provided with a thousand codices and organized by Francesco Petrarca. Used for a long time as barracks, provided in the Napoleonic period with a roofed raising that masks the battlement, in the twentieth century the castle was bought by the municipality, restored and used as cultural seat: indeed, it hosts the sections of the Civic Museums and rooms for temporary art exhibitions.