Home to Germany's oldest university, a castle ruin and an old town, Heidelberg is a must-see. For a great view of all this, cross over to the north side of the Neckar River, where the 440m (1,450ft)
Heiligenberg Hill offers a variety of trails. The Keltenweg, a circular walk, has a Celtic theme. It passes a defensive wall, monastery ruins and a medieval well. The Philosophenweg (Philosopher's Path), made famous by poets and thinkers, winds along the southern slope of Heiligenberg Hill. It passes gardens planted with exotic species such as Japanese loquat, Arizona cypress, Spanish broom and Portuguese laurel. A 4-km / 2.5-mile path links the Philosophenweg, the steep Schlangenweg alley, the Old Bridge and the main street of Heidelberg's old town.