Oddly, although I don't have one, I also think the 18-200 fits the best where any significant part of your trip is on a cruise. I've taken a one-day Rhine cruise with a 50mm and sorely missed a telephoto.
I've been fortunate to take a couple of additional European trips where the cruise(s) were limited, urban (London, Paris, Budapest) trips of just 1-2 hours. Those were enjoyable but minor elements of longer trips where the emphasis generally was more on City sights (museums, churches, etc) and my 16-85 was quite adequate (and very sharp)' and I tended to shoot within its limits by mostly being able to frame shots between 20mm and 70mm, maximizing sharpness and mitigating a bit of distortion at the wide end.
Have a great time and try to balance photography with recreation.