Southwestern Germany, in the state of Baden-Württemberg, brings together three quite different cities linked by train along the Rhine valley. Heidelberg sits on the banks of the Neckar, with the old center (Altstadt) squeezed between the water and the hill and the ruined castle looking down on the town. It is home to the oldest university in the modern country, founded in 1386, and it emerged from World War II almost undamaged.
Further south begins the Floresta Negra (Schwarzwald). It is not a park nor a single forest: it is a region of low mountains, about 160 km from north to south, covered with dark pines and firs (hence the name), cut by valleys, lakes, waterfalls and villages with timber houses. The highest point is the Feldberg, at about 1,490 meters. The region gave the world the cuckoo clock and the cake Floresta Negra (Schwarzwälder Kirschtorte).
Baden-Baden lies on the northern edge of the Floresta Negra and has relied on hot springs since Roman times. It has the Friedrichsbad, a 19th-century bathhouse, the Caracalla Therme, the Kurhaus with its casino and the Lichtentaler Allee, a park along the Oos stream.
Freiburg im Breisgau, at the southern tip, is a university city with a Gothic cathedral with an openwork tower, a daily market on the square and small water channels running through the streets (the Bächle). From there you can take the cable car up to Schauinsland and reach Titisee by regional train. The Triberg waterfalls, homeland of the cuckoo clocks, are just over an hour away.
This destination brings together 3 cities: Heidelberg, Baden-Baden, Freiburg im Breisgau.