Tanygrisiau is a village in the upper end of the Vale of Ffestiniog in the county of Gwynedd, North Wales (52°58′0″N, 3°55′60″W). It can be found along the southern side of the Moelwyn mountain range and dates to around 1750. It joins on to the semi-urban area of Blaenau Ffestiniog and is located between 650 and 750 feet above sea level.
The Moelwyns protect the village from much of the wind from northerly gales in the winter and give the village a pleasant southerly aspect with relatively mild weather considering its location high in Snowdonia. However rainfall in the upper end of the Ffestiniog valley can be very high all year around.
Tanygrisiau, or more properly 'Tan y grisiau' is Welsh (Cymraeg) for "below the steps", referring to steps, which have long since disappeared, leading up to the original slate mine above the village. Tanygrisiau was famous for its slate mining, producing a high quality black slate that was used all around the world.
The closure of the slate mines during the late 1970s led to massive depopulation of the area from which it has only recently (2005) begun to recover.
As a result of the slate mining, when the Snowdonia National Park was created, Tanygrisiau, Blaenau Ffestiniog and Llan Ffestiniog were left outside, thus creating a doughnut-shaped area excluded from the National Park.
Welsh is the predominant language of the area and the medium of instruction in all local schools.
Tanygrisiau has close links with the regiment of Welsh Fusiliers.
Tanygrisiau railway station is on the famous Ffestiniog Railway, a narrow gauge railway built to carry slate from the mines down to Porthmadog where it was shipped all around the world mostly for use in roofing. The nearby Ffestiniog Power Station, the high Stwlan Dam and the Tanygrisiau Reservoir are part of a pumped storage hydroelectricity installation. Much nearer the railway station is a waterfall on the Afon Cwmorthin and below the falls is a very small hydro-electric power station.
It is a good starting point for walks into the Moelwyns, especially if the intention is to climb Moelwyn itself. Care however should be taken as there are numerous mine shafts in the area.
Tanygrisiau was the site of a huge near disaster on Christmas day 1918. At the time when all the inhabitants of the village were in chapel the entire mine workings collapsed. Had this collapse taken place a few hours earlier, many hundreds of miners, newly returned from the first world war, would have died, instantly crushed to death under millions of tons of rock. Many of the inhabitants put this down to divine intervention.