@gumishu, this is the site of the former mine - it literally says "Nickel, chrysoprase and
opal mine in Szklary":
kopalniaszklary.pl/
Btw, chrysoprase has a pretty colour too :)
showcaves.com/english/pl/mines/SzklaryHuta.html
"The underground tour show quite exceptional bands of opal and chrysoprase in situ in the walls. That's the reason why it was declared a geotope. There is also an underground mineral exhibition with unique specimens of chrysoprase, you will probably see nowhere else. The shop sells jewelry which was created form the chrysoprase and opal from the mine."
As with the tours in Paulina's link, I'm guessing the tours are all in Polish language though?
I don't know to be honest. I did read in some article that foreign tourists interested in geology visit it too, so if they don't have tours in English that's a pretty big mistake, imho. Also, I didn't even know this place exists so they could do some better marketing too. 🤔
What is this?:

riddle8.jpg