Erdstall (tunnel)

Erdstall or erdställe (from German: erd, "Earth" + stall, "stall, stable") is a term for a type of human-built underground tunnel, typically very narrow, that was constructed in various locations across Central Europe, possibly during the Middle Ages. They are also known locally in Bavaria as schrazellöcher (German: "scratch holes") and zwerglöcher (German: "dwarf holes"), and in Austria as grufen, while similar structures in France are known as souterrains aménagés (French: "subterranean tunnels").

Resources

• (in German) Erdstallforschung - Unterirdische Gänge, erdstallforschung.de, https://www.erdstallforschung.de/ 
• (in French) Société Française d'Etude des Souterrains (SFES), subterranea.fr, https://www.subterranea.fr/ 

Reading

• Schulz, Matthias (2011-07-22), Experts Baffled by Mysterious Underground Chambers, spiegel.de, https://www.spiegel.de/international/zeitgeist/hideouts-or-sacred-spaces-experts-baffled-by-mysterious-underground-chambers-a-775348.html