The National Slate Museum is housed in the original Victorian workshops that maintained the enormous Dinorwig quarry — one of the largest slate quarries in the world — until its closure in 1969. The workshops are preserved essentially intact: the foundry, the pattern shop, the smithy, and the enormous waterwheel (the largest working waterwheel on the British mainland) that powered the machinery. Entry is free.
Daily demonstrations by quarrymen show the art of splitting slate — a skilled process of reading the grain of the rock and cleaving it into sheets of precise thickness. The introductory film is worth watching. The museum is part of the UNESCO World Heritage Site for the slate landscape of northwest Wales, designated in 2021. Allow at least two hours; the site is larger than it first appears.