Burgstein is a small rock formation in the Ilm valley near Langewiesen, east of Ilmenau. It is the kind of minor natural sight that makes sense when folded into a walk or bike ride through the surrounding villages.
Do not detour across Thuringia just for it. But if you are using Ilmenau as a low-key walking base, Burgstein adds variety to the forest-and-valley routes and gives you a reason to look beyond the obvious Kickelhahn circuit.