The Dinorwic Slate Quarry is a large former slate quarry, now home to the Welsh National Slate Museum, located between the villages of Llanberis and Dinorwig in north Wales. It was the second largest slate quarry in Wales, indeed in the world, after the neighbouring Penrhyn Quarry. It covered more than 700 acres (2.8 km2) consisting of two main quarry sections with 20 galleries in each and a number of ancillary workings. Extensive internal tramway systems connected the quarries using inclines to transport slate between galleries.
The first commercial attempts at slate mining took place in 1787, when a private partnership obtained a lease from the landowner, Assheton Smith. Although this met with moderate success, the outbreak of war with France, taxes and transportation costs limited the development of the quarry. A new business partnership led by Assheton Smith himself was formed on the expiry of the lease in 1809 and the business boomed after the construction of a horse-drawn tramway to Port Dinorwic in 1824. At its peak in the late 19th century, “when it was producing an annual outcome of 100,000 tonnes”, Dinorwic employed over 3,000 men and was the second largest opencast slate producer in the country. Although by 1930 its working employment had dropped to 2,000, it kept a steady production until 1969.