because of our age..wife and I are 73.. we would have appreciated a little more lounging time. we wanted to see everything and liked the idea of 1,2,3, ratings of guided tours, but perhaps during tours we would have a choice..ie during an extended tour (2+ hours) allow breakaway groups.
Bring very casual and comfortable clothes, and, of course super comfortable shoes. The streets are all cobble stone, very uneven surface, sneakers would work the best. Wear layers, so you can easily remove something or put on, as in the morning it can be plain cold, much warmer later on in a day.
Viking is very casual. It was cool to cold in Europe and raining several days. Just dress in layers and bring a rain jacket of some type. Viking provided umbrellas for every cabin if desired. Lots of walking if you take the included excursions. Demanding but not overly difficult.
Don't rely on the glitzy commercials that Viking puts on TV. It is not a fancy upscale cruise.