FWIW, Europe is pretty easy to do a lot of things without taking an excursion. I know on our trip, the only planned excursion we took was in Canakkale, where there really isn't much to do if you don't. Personally, I'd recommend taking a look at cruisecritic.com, and looking through their Europe forums. Even Florence you can probably do on your own if you're willing to take your chances with the Italian trains (the only real issue with them is they like to strike a lot).