At one time people were allowed to take boat tours on the salt lakes. Today, there are weddings in the salt cathedral, parties in a salt hall, and a health and wellness center underground, but the boat tours are not allowed- if there were ever actually any boat tours in the first place, but every tour comes with a tragic legend.
In some unnamed time, but well into the 20th century, there is a story about a group of young men, in a bachelor party, that rented a boat to tour on the salt water. They were very drunk and standing in the boat. As the boat passed into the tunnel one of the men hit his head and was knocked out of the boat and into the water. He was trapped between the boat and the side of the tunnel, and of course he drowned. To make the story more tragic he was the groom. I was told later by a Polish friend that the story is false. It does get a good reaction.