Baden-Baden, Germany

Baden-Baden sits in the Black Forest foothills along the Oos River, home to roughly 55,000 residents. The spa town has drawn visitors since Roman times, when an 80 AD bath complex delivered about 3,000 litres of 68°C water each day. Today the 2007 Caracalla Spa and the 1877 Friedrichsbad, with its 17-stage Roman-Irish thermal routine, continue that tradition, while the 3 km Lichtentaler Allee park lines the river on a route laid out in 1920. The 1877 Festspielhaus ranks as Germany's largest opera house, and the 1865 Kurhaus casino, rebuilt by Friedrich Weinbrenner in 1838, was once called the most beautiful in the world by Marlene Dietrich.