Uranium mine opened by Russians during occupation as a source of material for their nuclear weapons. They used Polish labour who worked unprotected and without knowledge of the dangers. They are now all dead ! Now converted into a museum mine. Visited by a group from Ireland and Shropshire in 2005.
Prior to this first it was a silver mine (XIVth century), then an iron mine (from XVIth century), and then a uranium and fluorite mine.
Now you can explore 7 adits of the mine: over 2 km long.
Pictures from Kletno:[url]http://tegroup.org.pl/exploration/galeria/kletno_galeria.htm[/url]