I have been to my share of mines and caves but never to a salt mine. This mine is massive and has entire underground lakes and even a chapel, with a beautiful Last Supper relief and altar and chandeliers all hand-carved from the salt walls - by tradesmen no less, not artists. They actually have mass in the chapel every week.
The massive salt deposits were what enabled the Polish kingdom to even be a thing. It was a huge economic boom.
Highly recommend a visit if you are in the area.