Idrija is a town in western Slovenia. It is the seat of the Municipality of Idrija. Located in the traditional region of the Slovene Littoral and 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. Together with the Spanish mine at Almadén, it has been a UNESCO World Heritage Site since 2012. In 2011, Idrija was given the Alpine Town of the Year award.

Mercury is a chemical element; it has symbol Hg and atomic number 80. It is also known as quicksilver and was formerly named hydrargyrum from the Greek words hydor (water) and argyros (silver). A heavy, silvery d-block element, mercury is the only metallic element that is known to be liquid at standard temperature and pressure; the only other element that is liquid under these conditions is the halogen bromine, though metals such as caesium, gallium, and rubidium melt just above room temperature.