These mines are a system of tunnels dug into the chalk under the city of Chełm in eastern Poland.
Chalk
The chalk mines exploitation started in the Middle Ages, and for hundreds of years, the tunnels were dug by the village residents. The chalk was then sold by the inhabitants. Years later, corridors were created and an underground system with chambers and halls was formed. The unintentional mines were dug up to 20 below earth level, and included several levels.
In the 19th century the chalk extraction ceases because the mine conditions began to endanger the village population safety. Many attempts were carried for reconditioning the tunnels for visitors. The first attempt was made in the interwar period, when the tunnels were rediscovered due to the water supply system installation. The Nazi occupation of the city caused the planned route destruction and the tunnels were used as a shelter for Jewish inhabitants.
After World War II, one of the corridors collapsed under the pressure of a truck driving under the street. This led to an underground exploration, where many underground corridors were discovered. Nevertheless, many underground tunnels remain undiscovered du to high risk and lack of money.
The Chełm Chalk Tunnels are unique in Europe and even the in the world. The connection of different tunnels and chamber occurred due to unplanned digging in different extraction points. The chalk “dungeons” are part of the town heritage and are mentioned in the inventories of the city inventories of the city dwellers’ possession during the 17th and 18th centuries. The exploitation stopped due to collapse risk.
Chalk is a limestone variety, mainly made of calcium carbonate derived from shells of marine animals and calcareous remains. It is usually white or grey, and is porous, permeable and friable. The extracted chalk is used for cement production.
In the 70s, some of the corridors were conditioned and reopened for visitors. Nowadays, the actual tour goes through three tunnels under the Old City Market Square. The visit is a 2 kilometres trail and lasts about 50 minutes. Many exhibitions can be found during the route, like the Old Town well or geological structures.
The chalk extraction ceased due to the risk it supposed to the Chelm environment and population. Now, its guided tour allows to appreciate the chalk chambers and tunnels: a true nature’s masterpiece.
A legend says that there is a defender of the underground halls: Bieluch, the “White Ghost”. If lucky, the ghost may be seen in one of the chambers.
https://en.wikipedia.org/wiki/Che%C5%82m_Chalk_Tunnels
https://web.archive.org/web/20080208074608/http://www.itchelm.pl/en/podziemia.html