This property includes the mining sites of Almadén (Spain) and Idrija (Slovenia). Together they represent the two largest mercury mines in the world
This postcard was sent by Stasa
Idrija is a town in western Slovenia. (...) It is located in the traditional region of the Slovenian Littoral and is in the Gorizia Statistical Region. It is notable for its mercury mine with stores and infrastructure, as well as miners' living quarters, and a miners' theatre.
Mercury was discovered in Idrija (known as Idria under Austrian rule) in the late 15th century (various sources cite 1490, 1492, and 1497). Mining operations were taken over by the government in 1580. The mineral idrialite, discovered here in 1832, is named after the town. - in: wikipedia
I'm still missing a postcard from Almadén, Spain