I did a 16 day Rick Steves tour of Germany, Austria and Switzerland back in 2002. Great tour back then. I wouldn’t chance it now.
We did a river tour on the Rhine and Moselle this past spring. I was very nervous when the boat was docked at night. Think of it--a glass-sided boat, docked at an unsecured pier. All someone would have to do is set a remotely detonated suitcase bomb. The river tourist traffic would evaporate the next day.