Bochnia is a town of about 30,000 people east of Kraków in southern Poland. Its salt mine, supposedly the largest in Poland, probably dates from the thirteenth century, and was once part of the royal salt works administered from Kraków. The mine was first accorded legislative protection in 1981, and it has subsequently been recognised as a national monument. In 2013 it became part of a UNESCO World Heritage Site when the designation of the mine at Wieliczka was extended.
The mines has 4.5 km. of galleries at 16 levels between 330 m. and 468 m. below the surface. The August Passage, almost 3 km. long, driven between 1723 and 1743 under the management of Jan Gottfried Borlach, provides access for visitors, and links a succession of chambers created by the extraction of salt. There are several underground churches in the mine, the largest of them the Chapel of the Blessed King, completed in 1782 as an enlargement of the Chapel of the Holy Guardian Angels of 1747. Some large wooden machines have been preserved, together with railways that were used for underground transport. The largest chamber, 225 m. long and 14.4 m. wide, is used as a sanatorium. The surface buildings of the mine and the headstock are well-preserved.