"Krzemionki", prehistoric flint mines (Poland)
Something of a coincidence!!! See this quote from my review of our visit to Spiennes Flint Mine last summer - "We then had another stroke of luck – at 4pm on that day a lecture was to be given (in English) by a visiting professor from the Polish Institute of Archaeology and Ethnology (who was assisting at the dig) titled the "Neolithic Flint Mines of Poland" and, since it was "free entrance", we thereby got in to the Centre for nothing!! Now, until I heard this talk, I just didn't know how much I didn't know about Flint Mining in Neolithic times!! Different types of flint and tools made from it, its geological origins, mining locations around Europe, different types of mines, trading and belief systems etc etc – as a result I have mentally "pencilled in" a visit to the Krzemionki mines (around 10kms NE of Ostrowiec) next time I am in Poland!! At least it seemed easier to get underground there! See http://krzemionki.pl/en/about-krzemionki/underground-route/ which says "The underground tourist route in Krzemionki is the world's only such monument open regularly to visitors."
How many different flint mines the List can take/needs is another matter - perhaps this is a case where Poland/Belgium should cooperate in creating a trans-national site covering both locations. As I remember the lecture I referred to above, "Polish Flint" is different in chemistry from "Belgian flint" and the mining technique was different too. If Almaden and Idrija can join together for Mercury mines and both get inscribed on the basis of slight differences between them, then why can't Belgium and Poland do so for Flint?? I note that there is absolutely NO mention of "Spiennes" in the write up - as if it didn't exist!