Final answer:
The Danube River is the second longest river in Europe, flowing through major European cities and emptying into the Black Sea.
Step-by-step explanation:
The second longest river in Europe is the Danube River. It flows through several major European cities, including Vienna, Budapest, and Belgrade, before emptying into the Black Sea. The Danube River is an important transportation route and has played a significant role in the history and development of Europe.