Wieliczka Salt Mines, Poland. Massive shoring of a giant cavern once filled with rock salt. Here we see huge support beams and posts. With such vast amounts of timber being used, fire was an ever present danger. The most serious fire occurred in 1644 and raged for 8 months. These mines experienced their golden age between 16th and mid-17th century. In this period the mining company employed about 2,000 miners, and production exceeded 30,000 tonnes.