The term 'River to the Rhine' refers to three rivers in Europe: the AAR (3 letters), the Ruhr (4 letters), and the AARE (4 letters). The AAR is a tributary of the Rhine that originates in the Swiss Alps and flows through Switzerland, Germany, and France. The Ruhr is a major river in western Germany that flows into the Rhine near Duisburg. The AARE is a tributary of the Rhine that originates in the Swiss Alps and flows through Switzerland and Germany. All three rivers eventually flow into the Rhine, which is one of the longest and most important rivers in Europe.