Introduction to the Wieliczka Salt Mine: The Wieliczka Salt Mine was built in the 13th century and has been continuously mined and provided salt to the Polish royal family. Once known as the world's oldest still-working salt mine, it is now out of use. The salt mine is 327 meters deep, over 300 kilometers long, and divided into nine levels, including more than 100 kilometers of tunnels. There are rooms, chapels, statues and underground lakes in the salt mine, just like an underground city. In 1978, the Wieliczka Salt Mine was listed as a World Heritage Site by UNESCO.