Ehrenberg is a wooded hill east of Ilmenau, opposite the university side of town. It is less famous than the Kickelhahn, but it gives a quick dose of local walking without turning the day into a full forest excursion.
Use it as a short escape if you are staying in town or visiting the university. The paths are not a must-see in the grand travel-guide sense, but they show why Ilmenau works well as a place to live: hills and trees are always close.