Großer Inselsberg is a mountain in the Thuringian Forest with a height of 916.5 m (3,007 ft) above sea level, located on Rennsteig in the districts of Gotha and Schmalkalden-Meiningen.

Großer Inselsberg is a rhyolitic butte that has withstood the weathering of the surrounding softer rock layers.

They are embedded in the conglomerates, sandstones and siltstones of the Goldlauter sequence to the north and the grainy gneiss of Cambrian origin to the south.

The potential natural vegetation of the mountain is a beech forest, on the northern slope with an undergrowth of heath bedstraw, on the sunny southern side with woodrush.

[1] The name is popularly ascribed to the solitary aspect of Großer Inselsberg and is said to be derived from German einzeln ("solitary") or Insel (Island), but is probably derived from a stream called Emse or in the Middle Ages Enze which has its source on the northwestern slope of the mountain.