Moelwyn Slate Quarry is a defunct slate quarry located to the south of the village of Tanygrisiau, north Wales. Some initial prospecting was carried out in the 1820s and again in the 1840s, but it was 1860 before a company was formed, and chambers were excavated. The quarry was never a financial success, and operated sporadically until its demise in 1897. Despite the poor results, a spectacular series of seven inclines were constructed, to enable slates to reach the Ffestiniog Railway. The quarry was hampered by lack of a good water supply, and the mill was constucted between inclines 4 and 5, where water could be obtained from Llyn Stwlan. As in many quarries, barracks were provided, but these were occupied by whole families, living on the mountain, rather than used as lodgings for the qu