Baden-Baden, is a spa town in the state of Baden-Württemberg, south-western Germany, at the north-western border of the Black Forest mountain range on the small river Oos, ten kilometres (six miles) east of the Rhine, the border with France, and forty kilometres (twenty-five miles) north-east of Strasbourg, France. In 2021, the town became part of the transnational UNESCO World Heritage Site under the name “Great Spa Towns of Europe”, because of its famous spas and architecture that exemplifies the popularity of spa towns in Europe in the 18th through 20th centuries.