The Vistula River is the longest river in Poland, and it flows through two major cities: Krakow (6 letters) and Warsaw (6 letters). Krakow is the second largest city in Poland and is known for its rich cultural heritage. It is home to the Wawel Castle, a UNESCO World Heritage Site. Warsaw is the capital of Poland and is the country's largest city. It is a major economic and political center and is home to many important landmarks, such as the Royal Castle and the Palace of Culture and Science.