Hi, we love Venice and have returned multiple times. Depending on what your group is not doing, you could go out to the nearby Murano, Burano & Torcello Islands by ferry. Burano is my favorite with the brightly colored homes & stores - wonderful for photography! Murano is the island where the beautiful glass is made.
My favorite gelato shop is Suso Gelato, and I’m picky about gelato - yum! Their Manet flavor is my favorite - pistachio cream & chocolate hazelnut layered. Also, the cherry cheesecake gelato. : )
When you’re in Venice, put away your maps & devices and just wander and purposely get lost. You’re in a maze of exploration with each left or right turn uncovering more interesting discoveries. When you get tired, stop for something to drink at an outdoor cafe, relax and then pull out your phone to see where you are. This is one of our favorite things to do each time! This is especially a great activity to do before you’re following a guide because it’s not the same when you’re just following the person in front of you.
My favorite way to enjoy an evening besides going to a classical concert at one of the churches is to sit at an outdoor table at Caffe Florian on the Piazza San Marco. Don’t go hungry! It’s expensive to eat there, so just go for an evening beverage. Relax with their 3-piece instruments playing atmospheric music while you watch the activity of the piazza waning with the sunset. Sit there for an hour, people watch and pinch yourself to believe you’re in such a special & unique location!
https://caffeflorian.com/
I won’t list the things to do that you can find in any Top 10 list on the internet.
For cities outside Venice, my favorite is Verona. It has a Roman Arena (small colosseum) that’s still used for music events, and the piazzas and historic center are very tourist-friendly. I’ve taken a city bike tour that was fun and also a cooking class. Take the faster train there. www.trenitalia.com. (Venezia S. Lucia to Verona Porta Nuova)
Ferrara has an interesting castle in the center of the city. Check to see that it’s open the day you’re going. Also, there’s an excellent museum, Museo Archeologico Nazionale di Ferrara with many displays of items uncovered at Spina. http://www.archeoferrara.beniculturali.it/
Vicenza would be lower on my priorities. It has the Palladio architecture in the city, a nice piazza and some interesting buildings outside of town. We walked out to the Villa La Rotonda besides enjoying the small center overnight.