If you want a fun experience and a view of Milan that takes your breath away (don’t worry you won’t have to walk all the way up there is an elevator) then you have to go up in the Torre Branca.
Right next to the museum Triennale di Milano is the 108 m tall Torre Branca which was designed by architect Gio Ponti in 1933. From its top you have a 360° panorama over the whole city. If there are strong winds or the weather is bad they are closed. It costs € 5,00 per person.
You could combine your vist with a visit to the Triennale museum and maybe even have lunch at the museum’s restaurant Terrazza Triennale. Or you could take a walk through the park and visit the Castello Sforzesco.