Salt was once one of the most valuable things in the world. Before fridges, salt was the main way people kept food from going bad. A mine that could produce salt year after year was worth more than gold, and the kings of Poland looked after Wieliczka very carefully.
Down in the mine, the air is thick with salt. The miners worked by candlelight, lowering themselves on long ropes. In their breaks they began carving the rock around them. Over many lifetimes they shaped whole chambers - some as big as a school hall - all out of salt.
The most famous chamber is St Kinga's Chapel. Everything inside it is salt: the floor tiles, the statues, the carvings on the walls, even the chandeliers, where each crystal is a polished piece of rock salt. If you lick the wall (and visitors do!) it really does taste like salt.
The mine has nine levels and over 300 kilometres of tunnels - longer than the distance from London to Manchester. Visitors only ever see a tiny part. Down at the bottom there are underground lakes so salty that people float on top of them, like in the Dead Sea.