The major river that flows through the capital cities of both **Hungary** and **Slovakia** is the **Danube River**. This river is the second longest in Europe, flowing through several countries before emptying into the Black Sea. In Budapest, the capital of Hungary, the Danube separates the historic sides of Buda and Pest, offering stunning views and numerous landmarks along its banks. In Slovakia’s capital, **Bratislava**, the river adds to the city's charm with waterfront attractions and recreational activities. The Danube is vital for trade, commerce, and cultural exchange in Central and Eastern Europe.