We will have three nights to stay somewhere from the date we leave the Cinque Terre and when we fly home from Milan. Any suggestions? We will be traveling by train.
Less than an hour, by train, from Milan is Lake Como. That's where I'm going when I arrive in Milan next year. Per others in this forum, we will stay in Varenna, and take a ferry to Bellagio.
Santa margarita ligure, stresa or lake como areas are all very nice but all quite diff from one another.
What else are you seeing on your trip? That will influence people's recommendations.
If you like big cities, don't overlook the option of spending a day or two in Milan itself (I personally like it a lot). On the other hand, if you don't like big cities, don't spend any more time there than you have to.
A good base for train travel is Bologna. I didn't like the city itself (although many do), but it's very convenient for day trips by train to Parma, Modena, Ferrara, Ravenna, and more.
I really liked my nights in Varenna on Lake Como, but Lake Maggiore is more convenient for Malpensa Airport, if that's where you're departing.
Do you like wine? Try the towns of Asti and Alba and get into Barolo or Babera d'Alba. They are south and west of Milano and south and eats of Torino