Truth be told, I don't remember a whole lot about the weekend trip I took to Milan when I studied abroad. I went with five of my roommates pretty early on in the semester, got to know them, and am happy to say four of them are still best friends of mine, and laughing my ass off with them is what I remember most. But aside from that...
So every Italian city has its Duomo, its main cathedral, and Milan's is LEGIT. The Gothic architecture is insane, and you won't see anything else like it. When we went, there was a random ice skating rink in the piazza out front, so that's how we spent one evening (yes, that picture is what it looks like -- I couldn't get the skates on by myself). We also saw Leonardo da Vinci's "Last Supper" at the Basilica di Santa Maria delle Grazie. Like the Sistine Chapel in Rome, standing in front of this is an indescribable experience. We visited Teatro alla Scala, the famous opera house, and L'Ultima Cena, a castle, just hangin' out in the city...because it's Italy.
It's obviously not the top tourist destination if you're visiting Italy on a schedule, but as you can see (accompanied by my overplucked sophomore-year eyebrows), it's beautiful in its own right, has delicious food (and limoncello, another sophomore-year discovery), lovely people, and makes for a kick-ass time with friends.