Heritage of Mercury. Almadén and Idrija is a joint UNESCO World Heritage site in Almadén, Spain, and Idrija, Slovenia. The property includes two mercury mining sites. In Almadén mercury has been extracted since antiquity, while in Idrija it was first found in 1490 AD. The Almadén site includes buildings relating to its mining history. These include Retamar Castle, religious buildings and traditional houses. The site in Idrija notably features mercury storage and infrastructure. It also includes miners’ living quarters, and a miners’ theatre. The sites shows how trade in mercury generated important exchanges between Europe and America over the centuries. The two sites represent the two largest mercury mines in the world and were working mines until recent times.