Ludwigshoehe and the Ludwigsturm give Darmstadt a quick escape into the wooded hills south of the city. The tower is the focal point, but the appeal is the whole outing: a walk through forest, a climb, and views back toward the city and the Rhine plain.
It is best in good weather and with walking shoes rather than as a drive-by stop. Pair it with the Mathildenhoehe if you want to balance Darmstadt's art-nouveau city identity with a dose of local landscape.