Sala was called ‘Seva rikes skattkammare’ (Sweden’s treasure chest). Silver mines discovered in the late 15th century were developed with the assistance of German miners. Until 1908 Sala was the country’s principal source of silver, and zinc production continued well into the 20th century. More than 30 mine buildings and structures dating from the 17th to the 19th century are preserved in the town, including several wooden headstocks. The museum offers a choice of three underground tours, one of them, in the Karl XI shaft, to a depth of 318 m.