The Externsteine are a sandstone formation in the Teutoburg Forest in Germany, near Detmold. The formation consists of several long stones, which rise abruptly from the hilly landscape. The stones are made of sandstone and originated in the Cretaceous period about 120 million years ago. The Externsteine are considered an attraction in North Rhine-Westphalia and also a breeding ground for a mystery. This is because traces of human use from the Middle Ages, possibly from prehistoric times, have been found.