The Danube, Europe's longest and perhaps most majestic river begins in the sleepy south western German hamlet of Donaueschingen; and winds its way upstream to the city of Ulm, which boasts Europe's tallest cathedral spire as well as being the birthplace of Albert Einstein, and then winds onwards through the lovely ancient and picturesque cities of Regensburg and Passau in Bavaria, the latter lying at the confluence of three rivers, below the Veste Oberhaus bishop's fortress and alongside the Austrian border.