Interesting models of machines invented/designed by Leonardo da Vinci. Also an excellent film that gives an historical context to his work. There are actually two da Vinci museums that show his machines, the other is on via dei Servi. Both are excellent. This one you can book online, the second one you pay at the counter in the shop and can actually make some of the machines work.

It is a great museum just 2 minutes walk from Duomo with cheap ticket(7€ adults and 5€ college students). It is small but it gives you all the information about Leonardo and his inventions, popular paintings, anatomy studies. You can touch all the invention and see actually how they work. The most impressive is that it was open on the 1st of January! There is also a wonderful shop outside. I would say that if you have an hour it totally deserves a visit.

Workable models of nearly every idea that Divinci had can be found in this museum. For those who have no interest in science or in history, I suppose they may not agree with me, but I believe this museum to be one of the better presentations of ingenuity in Italy.