One of the Walzwerk founders (Christiane Schmidt [2]) is from Saalfeld, a town very close to where I grew up. I've been to the restaurant a few times, usually with American coworkers, once with a friend from Saalfeld, so there was a lot of talk with Christiane that evening, and we went out with them after they had closed the restaurant. That was well over ten years ago though, almost fifteen, so I can't speak for the food they serve today. Back then it was quite authentic apart from the Thuringian sausages ("bratwurst thüringer art" on the menu [3]). They still were good, but you won't get Thuringian sausages outside Thuringia, impossible, even if many are labeled "Thuringian". No idea why, the recipe can't be
that much of a secret or too difficult. Anyway, the Walzwerk that I knew (until 2004) has my recommendation, since it's under the same ownership it probably still is a good destination :-)
I guess you know that, but just to add a few links for others, the name "Walzwerk" (translation: "rolling mill") refers to an East German steel factory [0] (very very dirty and run-down at the time of the reunification) about 15 miles from where I used to live. Today it looks a lot different [1] (like everything around that area - from lots of ashes, even ash mountains, and gray, to clean rivers and everything is orders of magnitude nicer).
[0] https://www.youtube.com/watch?v=oyxg9JUSkDE (German video)
[1] http://www.stahlwerk-thueringen.de/
[2] 2011: Article in the local Thuringian newspaper about the Walzwerk (German): http://www.otz.de/web/zgt/leben/detail/-/specific/In-einer-S...
[3] http://www.walzwerk.com/menu/