Heidelberg, Germany

Heidelberg sits on the Neckar River in Baden-Württemberg, Germany, with roughly 160,000 residents. The University of Heidelberg, founded in 1386, is the oldest university in Germany. Above the old town, Heidelberg Castle was built from the 1300s through 1622 and partially destroyed by French troops in 1693; its interior holds the 1751 Heidelberg Tun, the world's largest wine barrel at 220,000 litres. The 1788 Old Bridge spans the river on nine sandstone arches, while the philosopher's walk viewpoint runs along the north bank. Mark Twain chronicled his stays here in the 1880 book A Tramp Abroad.