River Rhine, the majestic German stream with all its symbolic and history, is the ideal place for decent river cruises. Be it for a day-trip or for a longer stay aboard in a hotel-like atmosphere. Many popular places can be visited without all the uneasy checking in – checking out procedures: Düsseldorf, Cologne, Loreley in the Mittelrheintal, Rüdesheim, Mainz and Karlsruhe are all Rhine cities and frequently attended by vessels.
Another point: Rhine cruises are cheaper than you might think, actually a very good value since they include a great part of your travelling costs, so e.g. no extra budget for train tickets is needed.