Tucked in a lovely valley between the Rhine River and the Taunus Mountains, Hesse's capital of Wiesbaden has long been an important spa city, dating back to Roman times when it was called Aquae Mattiacorum. In the 19th century, Wiesbaden also became a popular gambling center. For a soothing plunge, try the famous Kaiser Friedrich's Therme in the city center. And don't miss the Schlossplatz (Palace Square) and impressive Kurhaus Wiesbaden event and conference center, both within a few blocks.