250 million years ago, the whole of Central Europe was covered by the Tethys. The former inhabitants of this primeval sea can still be found today as fossils in the shell limestone in the Hainich. Rainwater penetrating limestone dissolves the lime and creates fissures in the subsoil. If such a cavity collapses, a sinkhole is formed on the surface.

In karst areas such as the Hainich, there is a lack of water as the surface water quickly seeps into the ground. In the past, a lack of water also prevented people from settling permanently in the Hainich. Geological and cultural aspects have contributed to the Hainich being a large, unfragmented forest area today - a UNESCO World Heritage Site.