Idrija was a centre for the mining of cinnabar ore, the ore from which mercury is obtained, for many centuries. Cinnabar deposits discovered in 1490 were worked by the government of the Habsburg Empire from 1509 and smelters were subsequently erected on the banks of the River Idrijca, north-east of the town centre. As many as 1,350 miners were employed in the area in the end-18th century. In the early 20th century a community of about 1,300 miners and their families was closely regulated by the mine management who provided employment in lace-making for the wives and daughters of the miners.
Visitors are able to explore Anthony’s Main Road, one of the oldest preserved mine entrances in Europe, which was dug in 1500. The tours extends 1,200 m into the mine where audio-visual shows and displays with replica figures illustrate methods of mining, and where visitors can see the underground Chapel of the Holy Trinity which dates from the mid-18th century when Idrija’s mines were at their most prosperous.
A museum in the Gewerkenegg castle, a building in Renaissance and Baroque styles that dominates the town, has as its principal exhibit a display entitled ‘Five Centuries of Mercury Mining’, but there is also a collection of the products of the local lace-makers and the new exhibition about mercury heritage, inscribed on UNESCO World Heritage List in 2012, entitled »Tracing Mercury: Idrija-Almadén«.