Munich is a pure example as it cannot be reached by boat at all.
There are companies offering river cruises.
And there are boats running by schedule on some rivers and lakes. But no overnight trips with these boats. Many of them had in the past (= before the trains) real transport tasks. Today they are however mostly touristic.
Dresden / Saxon Switzerland
Lake Constance is Germany's largest lake and in the warmer months has an extensive boat network to travel between the towns on the lake that are in Germany, Austria and Switzerland, and even a short way down the Rhine River to the falls. You can also travel between towns on the Chiemsee. Some of the rivers that have boat trips are the Rhine, Neckar, Main and Danube and there is limited travel along them between towns. I'm sure that there are other rivers where you can also travel short distances by boat.
Of course, you can also make multi-day cruises on those same rivers.
-:- Message from TripAdvisor staff -:-
This topic has been closed to new posts due to inactivity. We hope you'll join the conversation by posting to an open topic or starting a new one.
To review the TripAdvisor Forums Posting Guidelines, please follow this link: http://www.tripadvisor.com/pages/forums_posting_guidelines.html
We remove posts that do not follow our posting guidelines, and we reserve the right to remove any post for any reason.