The Goethehaeuschen is the little hut below the Kickelhahn summit associated with Goethe's "Wanderer's Nightsong." It is a small stop, but a memorable one if you know the poem or simply like the thought of literature pinned to a particular patch of forest.
Do not expect a major museum. Its value is in the setting: trees, slope, wind, and the gradual approach on foot. Pair it with the Kickelhahn tower and Jagdhaus Gabelbach rather than making it a destination on its own.