My wife and I are training from Lausanne to Genova and have never been in Milan - I was thinking of stopping enroute in Milan for lunch and a short look around … is it doable and worth consideration?
I think so. Easy tram and metro system links Milano Centrale other parts of the city. See the Duomo, get up on the roof, wander the Galleria.. Trams are fun. Let your eyes be the tourists...
If you are looking for a great restaurant in Milan, try Prime...here is the tripadvisor link:
https://www.tripadvisor.com/Restaurant_Review-g187849-d25192066-Reviews-Prime-Milan_Lombardy.html
I have eaten there twice and it was fantastic. Also, if I remember correctly, there is an "Eataly" store in the same neighborhood, just ask them at the restaurant, it would be fun to go in there and browse, maybe even have some wine or a gelato!
You can easily leave your luggage at the “deposito bagagli” (baggage storage) and wander around. Take metro (M3-Yellow line) to the Duomo (5 min ride).
See the Duomo, the Galleria, the La Scala Opera Theater. At walking distance there is also the Sforza Castle (museums inside).
That’s probably more than you have time for, especially if you have lunch, which in Italy is generally a 2 to 3 hour commitment of your time. The Last Supper at Santa Maria Delle Grazie is a little farther, and requires reservation, so you may not have a chance to see it.