There's an amazing salt mine near Krakow (I can't remember if it's detailed in the FCoK module) that's on UNESCO's list of World Heritage Sites.
http://www.wieliczka-saltmine.com/
I passed up an opportunity to go there in order to spend more time in Krakow itself. I can't decide if I regret that decision or not.
Salt's going to be extremely important in the T2KU because of its usefulness in preserving food. I can see it becoming like a form of currency. It has been used as such in the past.