River cruising in EUROPE  has become so popular companies have responded adding more modern riverboats & additional river opportunities. The RHINE river continues to be one of the most popular from Tulips in spring thru late fall as the season ends with the Christmas Markets passing castles, vineyards and multiple lock transits along the way. The DANUBE river stretches thru Eastern Europe from Passau to Bucharest offering a variety of combinations from 8 -21 days or longer, usually with pre or post stays in Prague, Munich, Nuremberg, Vienna, Budapest or Istanbul. In Russia the VOLGA river takes you from St Petersburg to Moscow. 
Now for some of the newer itineraries.  In France from Paris we have the SEINE river northward to Rouen allowing access the Normandy beaches or travel south on the SAONE & RHONE rivers thru Burgundy and Provence to the coast, offering great sightseeing, culture, food and wine. Many itineraries are easily combined allowing you to cruise throughout Europe as they meander joining East with West as seen on the map. The Venice lagoon and the POE river combines easily with a variety of land packages for perfect Italian vacation. To the west in Portugal the DOURO River flows thru gorges, hillsides and vineyards when added to Lisbon and/or Madrid land extentions for a relaxing Iberian experience.