Cave system and surroundings that represent some of the most significant Karst topography phenomena, including one of the world's largest known underground river canyons. The Karst area is of special importance in the history of earth sciences.
Prehistoric pile-dwellings settlements. Excavations in these sites have provided insight into life in prehistoric times during the Neolithic and the Bronze Age in Alpine Europe. Two sites in Slovenia are listed: the pile dwellings in Ig, northern group (kolišča na Igu, severna skupina), and the pile dwellings in Ig, southern group (kolišča na Igu, južna skupina). This is a transnational site that also includes sites in Austria, France, Germany, Italy, and Switzerland.
Idrija has one of the two largest mercury mines in the world, with mercury being first discovered there in 1490. The site features the infrastructure and technology related to mining and mercury production and bears testimony to the intercontinental trade in mercury, which generated important exchanges between Europe and America over the centuries. The site is shared with the mining town of Almadén, Spain.