The masterpiece of Gothic architecture in Italy. Its construction began in 1386 by will of Gian Galeazzo Visconti and continued for more than three centuries, attracting artists and craftsmen from all around Europe, while Italian, French and German architects alternated in supervision of works. The front was left unfinished up to the first decade of 19th century, when Napoleon Bonaparte ordered its completion.

The exterior of the building is decorated with 135 spires finely engraved, each surmounted by a stuatue, for a total of more than two thousands marble sculptures. The polygonal dome carries the highest spire, reaching 108 meters high, on whose top there is the famous golden statue of the Madonnina (Little Madonna), another symbol of the city of Milan. The cathedral's interior is dimly lit and its style is so sober to seem even bare when compared with the exterior, which produces an unfinished game of light and shade effects, thanks to the richness of its sculptural decoration.

Cathedral's interior, divided into a nave and four side aisles by more than 50 high pillars, is long about 150 meters. The transept, divided into three aisles, is instead 90 meters long. Both are decorated by wonderful stained glass windows, narrow and high, among which the most ancient belong to 15th and 16th century. The apse is the most lit area, decorated with three huge and magnificient glass windows with bent ribs and complex rosettes, performed by the French artist Nicolas de Bonaventura, under the coordination by the Italian architect Filippino degli Organi.

Main altar and chorus behind, work by Pellegrino Ribaldi, were done in 16th century. Inside the crypt is kept the silver urn with the relics by San Carlo Borromeo, archbishop in the 16th century and important figure in Milan history. Other notable monuments are: the mausoleum of Gian Giacomo de' Medici from the 16th century, the statue of San Bartolomeo, the bronze candelabrum, a French work from 13th century, and the cathedral treasure. In the cathedral building was incorporated the remains of the preexisting basilica and baptistery of early Christian age.

Inside the adjacent Royal Palace there is the exhibition of Cathedral's Museum, which illustrates the several stages of the construction and also keeps some statues, glass windows and tapestries. To be noticed a board crucifix from 11th century and the wooden model of the cathedral scaled 1:20, begun in the 16th century and completed in the 19th.