How did St Kinga make a salt mine appear in Poland? It's complicated. According to UNESCO, the legend goes like this:
Kinga, a Hungarian princess, was due to marry Duke Bolesław of Poland. They were both rich, so she didn't think it was important to bring money to the marriage. Instead, she asked her father to make her dowry up in salt.
This was difficult, as it would take an entire salt mine. Her father took her to visit a Hungarian salt mine to demonstrate the point.
Seeking God's advice, Kinga dropped her engagement ring into the mine shaft.
When she married, she moved to Poland and an amazing thing happened. She was touring her new estate and, at a certain point, ordered her men to start digging. They found huge salt deposits. To tell her of the find, one of her men presented her with a lump of white rock salt.
When she broke it open, encased inside was the wedding ring she had dropped into the Hungarian mine. She had miraculously brought a salt mine to Poland with her ring.
The salt found under there brought great wealth to her people, and Kinga was said to be a kind and just ruler. She was later canonized.