Aberllefenni Quarry
Gwynedd, United Kingdom · built 1400
Aberllefenni quarry is the collective name of three slate mines, Foel Grochan, Hen Gloddfa (also known as Hen Chwarel) and Ceunant Ddu, located in Cwm Hengae, just to the west of Aberllefenni, Gwynedd, North Wales. It was the longest continually operated slate mine in the world until its closure in 2003. Foel Grochan is the mine on the north side of the valley, facing Ceunant Ddu and Hen Gloddfa on the south; all three were worked as a single concern throughout their history. Rock was mainly extracted underground, though all three mines had open pits as well.
Mine data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).