Milan

Probably Leonardo's Last Supper, and the Duomo. Last Supper tickets probably not available now unless you book a city walking tour, which should include the Duomo.

See Cameron's recent blog entry about the possibility of last-minute Last Supper tickets: http://blog.ricksteves.com/cameron/2015/06/on-my-last-nerve-at-the-last-supper/.

In no certain order:
•Go to the Galleria Vittorio Emanuele across from the Duomo, find the ceramic tile "Toro" in the floor, place the heel of your shoe on his testicles, and spin for good luck. This is a very old Milanese custom. They have their sense of humor. It's easy to find as there is always a lot of people spinning and taking photos.
• Visit the Leonardo Science Museum and do not miss the aeronautical section. They also have an Italian Navy submarine, which requires a reservation.
* Go to the Navigli District for your after dinner passeggiatta (stroll). The area goes along a canal lined with bars, cafes, restaurants, and gelatorie.
• Visit the Gastronomia Peck on Via Spadero. It is the most upscale foodie shop in Milano. There is a 10,000 bottle wine cellar and upstairs is a nice cafe.
• "La Cenacola" - The Last Supper.

Buon viaggio,

Thanks to all for the tips.

The roof of the Duomo is a sublime experience, even in July heat.