Milan

The Duomo.

I don't know when you plan to travel, but keep on the top of the ticket situation for The Last Supper. They sell out.

Watch out for ZTL's.

What's a ZTL?

Milan has not a ZTL (limited access zone), but the central area (zona C) has access charges according to how polluting is the vehicle. Differently from a ZTL, you have a short grace period after the access to pay the charge, if you don't a fine is issued.

The best strategy there is leaving the car at one of the periferic interchange parking zones with the metro.

What's a ZTL?

It's a camera controlled area where non residents can't drive in without a permit. There is a ZTL in every italian settlement to protect historic centers from traffic and pollution. It's not a pedestrian area, if you live inside the ZTL you can get in.
If you don't know what a ZTL is... I really hope you haven't driven in Italy, yet.

The big problem is that the international sign used to mark the borders of ZTL areas isn't widely used out of Europe, so many tourists don't "see" it. In Florence they added signs written in English and red lights, but in small places where they see a couple of non European tourists per year... they can't even understand that some still expect to be allowed to drive anywhere!

Milan has not a ZTL

Milan has 2 ZTL areas:

• Navigli http://mediagallery.comune.milano.it/cdm/objects/changeme:56134/datastreams/dataStream1055612471031689/content?pgpath=ist_it_contentlibrary/sa_sitecontent/utilizza_servizi/mobilita/Regole_permessi/Autorizzazioni_ZTL/Zona%20a%20traffico%20limitato%20Navigli
• Sarpi http://mediagallery.comune.milano.it/cdm/objects/changeme:14412/datastreams/dataStream3921860870285097/content?pgpath=ist_it_contentlibrary/sa_sitecontent/utilizza_servizi/mobilita/Regole_permessi/Autorizzazioni_ZTL/ztl_sarpi_1

The one in Sarpi Street may be limited to vans and trucks, but I'm not sure.

There is also the congestion charge area (similar to the one in London) called "Area C".

If you can find a place to park, I'd recommend Milan for half a day. The Duomo is beautiful and the square is a great place to people watch. Just watch out for pickpockets. Its fun to take a stroll through the Galleria and see the expensive fashion stores. I did not get a chance to see The Last Supper but I have heard you must pre-book. You can also check out Sforza Castle.

Absolutely see The Last Supper! You have to get your ticket through a tour group - book well in advance. Milano's a great city to wander around. Duomo, main square, Galleria, Castle, shops, etc.

You don't need to get Last Supper tickets through a tour group, but the official site sells out very quickly.

If you miss the official site availability, you can buy tickets for Leonardo's Last Supper from a broker (about 100% over face value), without a tour, or buy a tour if you like.