The Danube River is the most popular and iconic destination for river cruises in Europe. Flowing through ten different countries, it offers an unparalleled diversity of culture, history, and scenery. Most classic itineraries focus on the "Upper Danube" between Budapest and Passau, passing through the Wachau Valley in Austria and stopping in majestic capitals like Vienna and Bratislava. The river’s popularity in 2026 is driven by its ability to dock right in the heart of these cities, allowing travelers to walk off the ship directly into world-class museums and cathedrals. The Rhine is a close second, famous for its "Romance" and high density of medieval castles, but the Danube's connection to the Habsburg Empire and its dramatic transit through the "Iron Gates" in the Balkans give it a slight edge for those seeking a comprehensive European experience. Because it is so popular, many lines now offer specialized "themed" cruises—such as Christmas Market tours or classical music voyages—making it a year-round powerhouse for the travel industry.