Across Europe, there are hundreds of underground tunnels that lead to nowhere and about which no historic records have ever been found. They are mostly located in the German state of Bavaria and the adjoining country Austria, where they are known by the German name “Erdstall”, which means “place under the earth”. Locally, they are also called by various names such as "Schrazelloch" (meaning "goblin hole") or "Alraunenhöhle" (meaning "mandrake cave") which reflects the various theories and legends associated with the mysterious tunnels.

Entry to the erdstall Ratgöbluckn at Perg, Austria. Its passages are high enough for touristic access. Photo credit: Pfeifferfranz/Wikimedia