1. Piazza Mercanti is the historic heart of Milan. It is a beautiful square surrounded by ancient buildings and filled with interesting statues and monuments. Originally a Roman forum, the square has been a center of commerce and trade since the Middle Ages. Today, it is a popular tourist destination and a great place to explore Milan’s rich history.

One of the most notable buildings on Piazza Mercanti is the Palazzo della Ragione, which was once the city’s courthouse. It is a large, rectangular building with a beautiful, arched portico facing the square. The palace also has a striking, sixteenth-century clock tower, which is a symbol of Milan.

Other interesting buildings on Piazza Mercanti include the Loggia degli Osii, an elegant, Gothic-style loggia that was once used for public debates, and the Casa degli Omenoni, a sixteenth-century palace with a unique facade featuring stone sculptures of muscular, male figures known as \"omenoni.\"

2. Piazza Mercanti is open to the public all day and night. There is no phone number available for the square itself, but the Palazzo della Ragione can be reached at +39 02 8846 4949.

3. There is no admission fee to visit Piazza Mercanti. The square is easily accessible by public transportation, and there are several metro and bus stations nearby. Visitors can take the metro to the Duomo station or the Cordusio station, or they can take bus lines 50, 58, or 94.