The Amazon River, winding through the heart of South America, is a marvel of nature that offers unparalleled adventure in one of the most biodiverse regions on Earth. Originating from the Peruvian Andes, the Amazon travels through nine countries before emptying into the Atlantic Ocean.

Coursing through 10 countries, the Danube is the second-longest river in Europe. This waterway, lined with fortresses and castles, rises in Germany's Black Forest and runs for 1,770 miles to the Black Sea. The Danube is an essential commercial thoroughfare for central and southeastern Europe, and several river cruise companies sail vessels on it year-round. Destinations along this river include Vienna, Budapest, Passau and Bratislava.