the trail
Section 8: Croesor to Tanygrisiau
Distance: 7.4km, 4.6mls Ascent: 470m, 1550ft Time; 3 – 4hrs
This leg is probably the wildest and most strenuous yet. A good track climbs the side of the Croesor valley to Croesor quarry. There are way marks but careful navigation is also needed to reach the remote Rhosydd Quarry, from where a broad track drops down to Cwmorthin Lake and its abandoned settlement. From here, the road drops down to Tanygrisiau.

Go along the road up the Croesor valley from Caffi Croesor, and take the broad track which climbs up the south side of the valley to Croesor quarry. After passing some derelict buildings, keep to the faint track which goes up between the ruins and climbs steadily, bearing left above the quarry. After a short while, follow the path across the dam of Llyn Croesor. Continue across sometimes boggy ground, aiming for a large white rock next to a stile. You are now above Rhosydd quarry.

Find your way through the quarry and take the broad track steeply down to Llyn Cwmorthin. Pass rows of derelict houses and the forlorn and roofless chapel, and take the track down alongside the tumbling river. At the houses, cross the river and walk down to the Lakeside Café at Tanygrisiau.

Along the way

Croesor quarry

Croesor Quarry was a large underground slate mine served by the Croesor Tramway. Small scale quarrying began in the 1840s, but it closed 40 years later.
In 1895, the quarry reopened under the direction of Moses Kellow, who set about modernising working practices and methods. He decided to electrify the works, building a hydro-electric station. He obtained motors from Prague, which were used to drive winches and an electric locomotive, the first to work in Wales. His greatest innovation was the Kellow drill, a hydraulic drill for which could drill a 7.5-foot (2.3 m) hole in the slate in under two minutes, much less than the day required using hand drills. The quarry closed in 1930.

The chambers were used by Cooke`s Explosives to store materials until the early 1970s. This ceased when the Central Electricity Generating Board became aware of it, and feared that an underground explosion would damage the dams of the Ffestiniog pumped storage power station. The Croesor -Rhosydd Through Trip is a well-known, if dangerous, route for mine explorers. The Snowdonia Slate Trail does NOT cross this bridge!


Rhosydd Quarry

Rhosydd Quarry was hampered by the remote location and transport was made difficult by the Cwmorthin Quarry, through whose land the route to the Ffestiniog Railway ran. A solution was found in 1864, with the opening of the Croesor Tramway, to which the quarry was connected by one of the longest inclines in Wales. The company went into voluntary liquidation in 1873.

The quarry was auctioned in 1874, and the New Rhosydd Slate Quarry Company Ltd was formed. The quarry prospered for a while, but then profitability declined, and in 1900, a large section of the underground workings collapsed. It was mothballed during the Great War and reopened in 1919, bought by members of the Colman family, of mustard fame. The quarry limped along and finally closed in 1948.
The quarrymen’s barracks were said to be the worst around – cold, draughty and unhygienic.



Cwmorthin has been quarried since the early 1880s. Despite significant output, the dangerous conditions underground and rock collapses led to poor financial performance and the mine changed hands many times.
Oakley Quarries of Blaenau Ffestiniog took over in 1930 and operated it until 1970, unable to pay to maintain the massive pumps running that kept the whole sprawling labyrinth dry. Throughout the 1980’s and early 1990’s Cwmorthin was working on a limited scale by a small team of local men. This endeavour too came to an end, with some unsuccessful attempts to untop the ancient Cwmorthin Slate Company workings around the year 2000 by McAlpines PLC.
What’s left to see today still comprises of many miles of tunnel and hundreds of enormous chambers. Within these workings can be found artefacts ranging from powder horns to timber stairways, from winches to wagons, and from cranes to bridges. The “Friends of Cwmorthin” group act as custodians of the mine today, aiming to promote its preservation, documentation and exploration.


Lakeside Café

The Lakeside Café, on the shore of Tanygrisiau lake provides a welcome refreshment break



Tanygrisiau is Welsh for “below the steps”, referring to the stepped cliffs above the village. Tanygrisiau was famous for its slate mining, producing a high quality black slate that was used across the world, transported by the adjacent Ffestiniog Railway to the sea at Porthmadog. Porthmadog exported vast quantities of slates all over the world. and the Porthmadog Maritime museum describe this in great detail. Porthmadog exported vast quantities of slates all over the world and the Porthmadog Maritime museum describe this in great detail.

The nearby Ffestiniog power station, the high Stwlan Dam and Tanygrisiau Reservoir are part of a pumped storage hydroelectricity installation

the trail

Section 1: Bangor to Bethesda

Section 2: Bethesda to Llanberis

Section 3: Llanberis to Waunfawr

Section 4: Waunfawr to Nantlle

Section 5: Nantlle to Rhyd Ddu

Section 6: Rhyd Ddu to Beddgelert

Section 7: Beddgelert to Croesor

Section 8: Croesor to Tanygrisiau

Section 9: Tanygrisiau to Llan Ffestiniog

Section 10: Llan Ffestiniog to Penmachno

Section 11: Penmachno to Betws y Coed

Section 12: Betws y Coed to Capel Curig

Section 13: Capel Curig to Bethesda

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