Penrhyn Quarry
United Kingdom
The Penrhyn quarry is a slate quarry located near Bethesda, North Wales. At the end of the nineteenth century it was the world's largest slate quarry; the main pit is nearly 1 mile (1.6 km) long and 1,200 feet (370 metres) deep, and it was worked by nearly 3,000 quarrymen. It has since been superseded in size by slate quarries in China, Spain and the USA. Penrhyn is still Britain's largest slate quarry but its workforce is now nearer 200.
Data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).