The Rennsteig is a ridge walk, as well as an historical boundary path in the Thuringian Forest, Thuringian Highland and Franconian Forest in central Germany.
In the Middle Ages the Rennsteig marked the boundary of the Duchy of Franconia with the Landgraviate of Thuringia. Even today it forms a clear border between the Franconian part of South Thuringia from the otherwise overwhelmingly Thuringian-Upper Saxonstate of Thuringia. The Rennsteig is the language border separating the East Franconian dialects of Hennebergisch, Itzgründisch and Upper Franconian from the Thuringian dialects of Central Thuringian, Ilm Thuringian and Southeastern Thuringian, which is spoken in the mountains, in northern parts and east of the Thuringian Forest. The Rennsteig is also the watershed between the river systems of the Werra/Weser, Saale/Elbe and Main/Rhine. The catchment areas of all three river systems meet at theDreistromstein (Three Rivers Stone) near Siegmundsburg.
Today the Rennsteig is designated by the German Mountain and Hiking Club (Verband Deutscher Gebirgs- und Wandervereine) as an outstanding high-grade hiking trail. It was discovered by August Trinius for the hiking fraternity and became famous well beyond the borders of Thuringia and Franconia mainly through the publications of the Rennsteig Club founded in 1896. The Rennsteig Cycle Way was opened on 19 June 2000. Most of it is provided with a water-bound surface, some sections also run along quiet country lanes. Here and there it departs from the course of the historic Rennsteig, so that steep inclines may be avoided. It is therefore about 30 km longer than the hiking trail.
The Rennsteig runs along the ridge of the Thuringian Central Uplands from northwest to southeast mostly at heights of around 500 to 970 metres. It begins in the Eisenach town quarter of Hörschel by the River Werra (196 m above NHN) and ends after 169.3 km in Blankenstein by the River Saale (414 m above NHN). In 2003 the Rennsteig was re-surveyed by the Thuringian State Office for Survey and Geoinformation; they reported that it had a total length of 169.29 km. The marking along the trail is very good, usually indicated by a white R. Along the Rennsteig there are small, open shelters about every 5 to 10 kilometres.
In the winter, in good snow conditions, langlauf skiing or hiking in snow shoes is possible and the Rennsteig is maintained as a winter hiking trail in places.
The course of the Spitter stream, the only river in the central section of the Rennsteig, crosses the trail in the Ebertswiese nature reserve, at a height of 700 metres, before feeding the nearby Spitter Waterfall. Another stream that crosses the trail is the Dober in the southeastern part of the route, which forms part of the Franconian Forest immediately by the Thuringian-Bavarian border west of Brennersgrün, part of the borough of Lehesten.
Three tunnels run under the Rennsteig: One is the eponymous Rennsteig Tunnel, which is in fact two tunnels that are 7916 and 7878 metres long, making it the longest road tunnel in Germany. The tunnel was opened in 2003 as a motorway tunnel for the A 71 autobahn. The second is the 3039 metre long Brandleite Tunnel, which was opened in 1884 and leads the Erfurt-Schweinfurt railway under the Thuringian Forest. Both tunnels only have a vertical height difference of seven metres between each end. The third is the 549 metre long Förtha Tunnel on the Werra Railway.