River Cruises
River cruising, especially in Europe, has become very popular with Americans in the last 10 years. It's a great way to visit the cities along the rivers and, like all cruising, you get to take your hotel (and all your stuff) with you.
History - river cruising has been popular in Europe for many years. When Americans first started to experience it they found the cabins to be small, smoking was everywhere, most announcements were in a foreign language, and most of their traveling companions could not speak English. Today, ships are new, cabins are larger, many lines cater almost exclusively to English speaking people (Americans, English, Australians, and Canadians), smoking is limited to outside deck areas, and announcements are exclusively in English.
Companies - there are really four companies involved in the European river cruise market with two others that would be classed as luxury options - Viking (probably the largest), Uniworld, Avalon (part of Globus), and AMA Waterways. The luxury lines are Scenic and Tauck. Aside from the luxury orientation, there is not a lot if difference among all of these organizations.
Itineraries - the ships sail all the rivers of Europe - the Rhine, Danube, Seine, and others. You visit cities such as Amsterdam, Budapest, Cologne, Nuremberg, Paris, Prague, and Vienna as well as small medieval towns that grew up along the rivers.