Danube

From World Wikia

Danube River: Vienna and Budapest are connected by The Danube, and during tourist season, when it is warm, there are high speed hydrofoils and slower pleasure boats that ply the waterway. If you’re heading to Vienna, this can be a great way to get to the next stop on your itinerary. If you have an extra day to spend in Budapest, you can travel up “The Danube Bend” to Visegrad Castle (an early residence of Hungarian Kings with a spectacular view of the river), Szentendre (a tiny artist community), and Esztergom (the seat of the Hungarian Roman Catholic Church and its most magnificent Cathedral).