A very interesting and surprising environment awaits if you visit the Wielicki salt mines which are about 45 minutes outside of Krakow.
On arrival you walk down 183 metres with a couple of stops along the way. The climate is controlled at 15 degrees via hermetically sealed doors and the ceiling soar above you even though you are so far underground (and in fact the mines go down to 300 meters). These mines have existed since the 14th century and were only closed about 15 years ago.
Aside from actually being surrounded by massive rooms, they are full of sculptures – most done by the miners – all in salt. There is a chapel and a huge ballroom used for concerts and weddings and even the chandeliers are made of salt crystals. The last supper below is actually only six inches deep but has amazing perspective.
Here is the wedding/concert hall and the chandelier.