Гисен

Gießen has the highest density of students of any city in Germany — roughly one in three residents — and the laboratory where modern science teaching was born. Justus Liebig held his chair here from 1824, revolutionising chemistry by the simple, radical act of putting students at the bench: his institute became the model for research universities everywhere, and survives as the Liebig Museum, the original laboratory preserved with its furnaces, flasks and lecture theatre — a shrine chemists visit the way musicians visit Bayreuth.

The scientific lineage runs deep. Wilhelm Conrad Röntgen held his first full professorship in Gießen and, by his own wish, lies buried in the Old Cemetery; the university, founded in 1607 and now bearing Liebig's name, keeps a botanical garden established in 1609 — the oldest in Germany still on its original site. The tradition turned playful in 2002 with the Mathematikum, the world's first hands-on mathematics museum, where visitors stand inside soap bubbles and walk through number theory.

War razed three-quarters of the old town, so Gießen's charms are collected rather than continuous: the half-timbered Burgmannenhaus and Leib'sches Haus with the upper Hessian museum, the Botanical Garden's green heart, the Stadttheater of 1907 — a handsome Jugendstil-edged house whose opera, drama and concerts serve the whole region — and the Lahn's meadows threading it all together. A city that thinks for a living, and always has.