The Externsteine is a distinctive sandstone rock formation located in the Teutoburg Forest, near the town of Horn-Bad Meinberg in the Lippe district of the German state of North Rhine-Westphalia. The formation is a tor consisting of several tall, narrow columns of rock which rise abruptly from the surrounding wooded hills.
In a popular tradition going back to an idea proposed to Hermann Hamelmann in 1564, the Externsteine are identified as a sacred site of the pagan Saxons, and the location of the Irminsul idol reportedly destroyed by Charlemagne; there is however no archaeological evidence that would confirm the site's use during the relevant period.
The stones were used as the site of a hermitage in the Middle Ages, and by at least the high medieval period were the site of a Christian chapel.
- Wikipedia