Ilmenau is best when you treat it as a town-and-hills destination. Spend a little time around the market square and St. Jakobus Church, then follow the Goethe associations uphill toward Jagdhaus Gabelbach, the Goethehaeuschen, and the Kickelhahn lookout tower.
The Technische Universitaet Ilmenau gives the town its contemporary life, while the surrounding ridges offer easy access to the Thuringian Forest. The walking is the point: you do not need a long expedition, just a free afternoon and enough energy for the climb.