https://en.m.wikipedia.org/wiki/ErdstallErdstall
An erdstall is a type of tunnel found across Europe. They are of unknown origin but are believed to date from the Middle Ages. A variety of purposes have been theorized, including that they were used as escape routes or hiding places, but the most prominent theory is that they served a religious or spiritual purpose.
Etymology
There are very few historic references – a document from 1449 names the area above the tunnels as "auf den erdstelln". Although the modern term uses "Stall" (stable, shed) it is in fact related to "Stelle" (spot, location – cognate to English "stead") along with "Erde" (soil, ground – cognate to English "earth"). The German "Stollen" (tunnel in mining) has the same origin.
Alternative regional names are "Schratzlloch" (Bavaria), "Zwergloch" and "Grufen" (Austria) that carry the regional names for dwarfs that folk belief has connected them to.
Construction
The erdstall tunnels are very low and narrow – they have a height of 1.0 to 1.4 metres (3 ft 3 in to 4 ft 7 in) and a maximum width of about 60 centimetres (24 in). Additionally they feature very tight passages from one tunnel to a lower tunnel called "Schlupf" (slip out) that is too narrow for older or overweight persons – a person needs to crawl under the slip hole, stand up thereby sliding the shoulders through the skin-tight hole, allowing to crawl onto the higher tunnel.
Erdstall tunnels have only one narrow concealed entry point – so there is no second exit tunnel as with an escape tunnel system. Some tunnel systems feature loop tunnels at the end of a tunnel. Most tunnel systems are not longer than 50 metres (160 ft).
Archaeology
There is almost no archaeological material to be found in the tunnels although erdstall tunnels exist in abundance in Central Europe (over 700 in Bavaria alone). This makes it highly unlikely that they were ever used as dwellings, such as a hiding place in times of war.
The archaeological evidence is so slim that even age determination is difficult. Coal from a fire pit at Bad Zell has been dated between 1030 and 1210. Coal from a heading in Höcherlmühle has been dated between the late 10th and mid-11th century. A slip passage at Rot am See has been enhanced with stones to make it narrower with the stone additions dated to between 1034 and 1268. Coal from Trebersdorf was dated 950 to 1050, coal from Kühlried was dated to 950 to 1160. Ceramics found in St. Agatha have been dated to the 12th century which seems to be the latest date of usage.
Some pics (not for claustrophobics):
Long discussion thread on Reddit, if interested: https://old.reddit.com/r/UnresolvedMyst ... _be_found/
Long rambling article in the Spiegel. I'll extract this interesting point:
It is clear, at any rate, that they were built by professionals. They dug the tunnels in a kneeling position, using wedge-shaped tools held with both hands. Every few meters, they chiseled cavities into the walls for their oil lamps. They dug the longer passageways in serpentine form to reduce the pressure from the surrounding earth. Supporting planks were not used.
Around the year 1200, the underground labyrinths were filled in and the entrances blocked with rubble. The rubble contained ceramics clearly attributable to the Gothic period.
). My impression is that as they are just holes in the ground without artifacts (which already excludes a lot of possible uses – or perhaps even any use at all) they haven't interested archaeologists apart from local amateurs.