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. The long-distance trail stretches about 170 km (110 miles) from Eisenach and the Werra valley in the northwest to Blankenstein and the Selbitz river in the southeast.
The Rennsteig is also the watershed between the river systems of the Weser, Elbe and Rhine. The catchment areas of all three river systems meet at the Dreistromstein (Three Rivers Stone) near Siegmundsburg.
The Rennsteig runs along the ridge of the Thuringian Central Uplands (Mittelgebirge) from northwest to southeast mostly at heights of around 500 to 970 metres. It starts in the Eisenach town quarter of Hörschel by the River Werra (196 m above NHN) and ends 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 (105.19 miles). The marking along the trail is very good, usually indicated by a white 'R' (called Mareile). Along the Rennsteig there are small, open shelters about every 5 to 10 kilometres.