The Thuringian Forest (Thüringer Wald in German) running northwest to southeast, forms a continuous stretch of ancient rounded mountains posing ample difficulties in transit routing save through a few navigable passes in the southern reaches of the German state of Thuringia. It is about long and wide. The highest elevation is the Großer Beerberg, .
The Rennsteig (sometimes called Rennweg) is an ancient path following its summits along the main ridge. It is now a famous hiking path and it marks the traditional boundary between the hills-dominated terrain of central Germany and the more rugged terrain characteristic of southern Germany, the boundary between central/north Thuringia and Franconia. Dialect, and traditional customs and costumes were different on either side of the Rennsteig. The Rennsteig is also subject to the song Rennsteiglied, the inoffical hymn of Thuringia.
The Thuringian Forest is famous for Wartburg Castle outside Eisenach (where Martin Luther stayed for some time in exile) and year round tourism, including many winter sports resorts. In modern literature, the forest has become famous as a nearby local and strategic barrier for the fictional towns of Badenburg and Grantville, WV in the popular alternate history book series that began with Eric Flint's 2000 novel 1632, one act of which involved a battle at the Wartburg, and its destruction, and a cavalry raid mounted through the Forest by Catholic forces in the setting during the Thirty Years' War, as influenced by the town.
Geologically, the Thuringian Forest is defined by a belt of strongly uplifted and deformed metamorphic and igneous rock that divides the relatively flat sedementary plains of the Thüringer Becken (to the northeast) from similar rock formations in the valley of the Werra (to the southwest). The Schwarza River, following the axis of the Schwarzburg anticline (Schwarzburger Sattel), divides the Thuringinan Forest from the slate hills of Thuringia and Franconia, to the southeast Ore deposits associated with this upthrust have been of significant historical importance in the development of the region, for example, in Suhl and Ilmenau
Sunrise on the mountain Ruppberg near Zella-Mehlis (Thuringian Forest, Germany)