The Grüne Tanne (Green Fir) is Jena's most historic inn, a Gasthaus at the east end of the Camsdorf Bridge that has been serving food and drink since at least the eighteenth century. The building has survived wars, floods, and reunification, and retains the feel of a genuine old inn rather than a themed recreation.
It is the traditional starting or finishing point for walks up the Jenzig, and walkers arriving back from the hill in the late afternoon have been doing exactly what you're about to do — ordering a beer and a plate of Thuringian food — for two hundred years. The menu leans on regional classics: Thüringer Klöße (potato dumplings), roast meats, and the local Rostbratwurst. The terrace has views of the Camsdorf Bridge and the river.