Sforzesco Castle & Sempione Park & Gate of Peaceviews: 1846
There is a museum inside the castle.
There is also a large Sempione Park nearby, so take a leisurely stroll. At the end of the park is the Arco della Pace (Peace Gate / Arc de Triomphe).
Most of all, I went to see the unfinished work of <Rondanini Pieta>, the last work of Michelangelo. It is said that he worked on the work until his death in his late 80s.