Unique or little gem things to see or do in Milan

Go to the Navigli neighborhood south to the city center for "Happy Hour" bar food sampling. The food is free when you buy a glass of wine. It is around the last sections of the old city canal network. Interesting lively neighborhood.

See if either AC Milan or Inter Milano have a game at San Siro stadium while you are in town.

I like Sam's suggestions.....here's another......a tour of the Alfa Romeo museum in nearby Arese.

Hi Suzannebell,
I have spent quite a bit of time in Milan in 2015 and 2016 and off the top of my head, I can recommend seeing:
The Duomo (see the crypt behind the pulpit too) also, you can climb to the top of the cathedral and walk among the spires at sunset -- really cool and makes for wonderful pictures!
See the Galleria Vittorio Emanuele II if for no other reason but to see the mosaic bull on the floor and put your heel in the worn area of the bull's private parts and spin yourself around for good luck (or watch all the other people do it.)
Make a reservation and see The Last Supper at the Church of Santa Maria delle Grazie.
Leonardo da Vinci's vinyard (it opened back up for people to see in 2015.)
The Omenoni is a treat to see, if you like architecture, also there are great monuments to see in the various piazzas.
The Sforza castle and the fountain in front of it, just walk around and go behind it to the Parco Sempione see the Arco della Pace at the end of the walk through the park and skip the museums in the castle if you're tired of museums,
I loved Milan and found lots of things to see and do while there, I used the metro exclusively. Sorry if these things are already on your list to visit. Enjoy your time in Milan!

Chiesa di San Bernardino alle Ossa: built near the area of a former hospital cemetery, the walls of a chapel are decorated, ground to roof, with human bones found overflowing from collettive graves. Good for an horror movie.

We loved the Cimitero Monumentale di Milano and will go back because we didn't see more than half of it. Look at Google Images of the large, dramatic, idiosyncratic sculptures to see if you would like this sort of thing. Life-size oxen, for instance. And it's very peaceful.

Go see the Chiesa di San Maurizio al Monastero Maggiore. It's been dubbed the Sistine Chapel of the North. Amazing little gem when we visited last year.

I enjoyed the tour of La Scala and its museum. The Sforza Castle is impressive and has several small interesting museums. And lots and lots of stairs.

Monument Cemetery - an easy metro ride, beautiful sculpture and monuments, landscaping. Peaceful, park like setting, really breath taking. Also recommend booking in advance to see The Last Supper. I also went to a concert at La Scala, the opera house. Old world elegance, was the only non-Italian, I believe/heard, night I was there. Thoroughly enjoyed.

Another vote for Cimitero Monumentale di Milano - we spent several hours there and it was amazing.

The San Maurizio church is a real Jewel and such an interesting history!