Wieliczka Salt Mine or "Kopalnia soli Wieliczka" was built in the 13th century and it is one of the world's oldest salt mines still in operation until 2007.
It is also referred to as "the Underground Salt Cathedral of Poland" due to its three chapels and an entire cathedral carved out of the rock salt by the miners and placed on the UNESCO list of the World Heritage Sites in 1978.
The mine is one of Poland's official national historic monuments.