Town for 3 nights between Venice & Milan

Bergamo is lovely, but I would pick Verona. (You're not going to take the train into Milan the same day you fly out of Milan, are you? What if the train is late?)

As far as larger cities, you have your choice of Verona and Brescia. You could also go into Milan and take a short train ride up to popular Lake Como area.

11 nights in Venice?? I always recommend giving Venice several nights, but 11 is even too much for me.

Tim, It’s all happening in Venice mid-September to mid-October. The Architecture Biennale, so that is four days taken care of, and also the Homo Faber exhibition on San Georgio, displaying the finest craftsmanship you could ever hope to see, and so that’s another couple of days.
Day trip to Padua, the Tre Oci photo gallery, the Querini, maybe a trip to see the Brion tomb at Altivole, picnic on Certosa, maybe the Gypsoteca at Possagno showcasing Canova’s plaster casts. Easy to burn up ten days before you know it.
We are staying in an apartment on Giudecca rather than in the main part of Venice where we previously stayed, so that will be different, a lot of vaporetto trips I anticipate.

Verona is lovely. I don't know Bergamo. Another possibility is Bologna, though it looks "out of the way" on a map, the travel time difference is negligible. . . . 1-1/2 hours from Venice, 1-1/4 hours to Milan.

Another vote for Verona. A really great small city in which to spend a few days. While there a short day trip to Vicenza would be quite doable and interesting.

1 would also choose Verona. I've stayed there twice and really enjoy it.

Bologna.
We loved it.

I am going to agree with the vote for Bologna. We followed advice here a few years ago and spent three nights in Verona. Although we loved the countryside and Valpolicella, Verona just didn’t click for us. Bologna is the foodie capitol of a foodie country. 😊

Vicenza is the birth place of Palladian Architecture
https://en.wikipedia.org/wiki/Andrea_Palladio

All good suggestions, Verona, Bologna and Vicenza, all great cities, or towns for Vicenza.

We have stayed in Bologna, really enjoyed the meridian line in the cathedral and the Focault pendulum that demonstrates that the earth rotates. In the sacristy are models and drawings of how the cathedral might have looked.

Verona is special for us too. Three nights on our first trip to Italy, and several nights more recently. The Castel Vecchio is a superb museum, also a showcase for the work of my favourite Venetian architect, Carlo Scarpa. We walked a bit up into the hills with a picnic; if you want to get a handle on a city, always walk uphill. (Does not work for Venice, on account of a lack of hills other than a couple of mounds in the Giardini.)

And Vicenza is a lovely small town, with bits of Palladio’s work scattered around. The Palladio museum is great, in that it explains why Palladio’s designs “work”, taking into account the way light falls across architectural details.

So we are still thinking about where to spend the nights. Can’t go too wrong in Italy, I suppose.

Aussie, mate.

Have been in the region for mid-autumn. Lovely autumnal colours that we don’t have. I have only driven to Bergamo, so don’t have experience with the rail or local transport arrangements. Have spent about 4 hours in the old town. Largely unmolested by modernisation. Has interesting middle ages buildings. Can’t recall architectural styles. Did not know much about town before we went there, but in hindsight would have been worth more time. Drove through the lower city and did not stop.

May I suggest Largo Maggorie for consideration. Particularly Stresa. Normally quite serene in autumn. A relaxing ferry cruise around the lake and the Borromean Islands. Cable car ride to top of Mount Mottarone with, on a clear, day great vistas north toward Switzerland.

I assume afternoon or evening flight out, so should be no worries getting to airport on time.
Have a great time at the biennale and other displays.

Regards Ron