Nyth-y-Gigfran quarry (sometimes spelt: Nith-y-Gigfran or Nidd-y-Gigfran; sometimes known as Glan-y-Pwll quarry) was a slate quarry in the town of Blaenau Ffestiniog, North Wales. It was located about above the settlement of Glan y Pwll, south of what was to become Blaenau Ffestiniog. The quarry was sited on the steep cliffs that form the eastern edge of Allt-fawr and was entirely underground. The quarry opened c.1846 and became part of the Oakley quarry in the 1880s; this in turn closed in 1969.