The Visconti's first historic outpost of the possessions of the Republic of Venice, Trezzo sull'Adda is a village which still preserves its medieval features. It is situated in the territories of Milan, in a large Park, at North of the River Adda, where the river creates a double bend. Some historians argue on the origins of its name, which seems to derive from the Celtic word "trec" (cape).
The Celts, probably, were the first inhabitants of the area, confirmed by some archaeological finds, including a "sistula" (metal pot) discovered in 1846. After the fall of the Roman Empire, Trezzo was ruled by the Lombards, whose presence is revealed by the presence of five tombs with a lot of funeral dowry items, found in the district of San Martino. It was during this time that decision was taken to fortify the cliff by the Adda and so the first fortress of Trezzo was built, ordered according to the traditions by Queen Teodolinda. Subsequently, the country became part of the dominion of the Visconti, who made it a cornerstone of their defensive system.

Among the major sites of interest:
- The Visconti Castle, built by Bernabo Visconti in 1300 next to the fortified tower which the traditions retain was built by Teodolinda and it is located on a rocky outcrop overlooking the Adda. At present it is possible to visit the dungeons and the imposing tower.
- the hydroelectric plant Taccani, built in 1906, a classic industrial building in Art Nouveau;
- The Sanctuary of the Madonna del Carmine, in the district of Concesa, in neo-Gothic style. Built to preserve a fountain that springs water with attributed miraculous properties;
- The provostal Church of Saints Gervasio and Protasio, dating from the XV century, with frescoes of the famous Italian artist Giotto ;
- The Oasis WWF "Le Foppe, a natural environment, which preserves within its borders a series of ponds, meadows and wooded areas.