The mining history in Idrija goes back to 1490. At its peak, it was one of the main sources of mercury, along with Almaden, in Spain. Mercury is a rare metal and its deposits are scarce. Most of it is in the form of ore known as cinnabar (mercury sulfide). Idrija is one of the very few places in the world where mercury occurs in both its elemental liquid state and as cinnabar.
Mercury can be used to extract silver and gold, therefore the silver and gold-rush motivated mercury mining. Most of the history and development of Idrija revolves around mercury. The mining industry brought science, technological advancements, and industry to this mountainous region but it also created considerable medical problems and health hazard due to its toxicity. In addition to collapse accidents, there is a local folklore associated with hallucination experiences that miners had when working in the narrow passages inside the mountains.
About the source
Atlas Obscura aims 'to inspire wonder and curiosity about the incredible world we all share'. You can contribute to their collection on their website.