Moelwyn Mawr means Big White Bare Hill, according to go4awalk, and its summit stands at 770 m.

You can climb it from Tanygrisiau on the east or from Croesor on the west.

From Tanygrisiau, The Great Outdoors magazine goes up through the Cwmorthin quarry ruins. From Croesor, Walking World climbs the grassy west ridge.

Stay on the paths wherever old quarry ground lies beside the route.

How high Moelwyn Mawr is

Per go4awalk, Moelwyn Mawr is 770 m (2,527 ft), and its summit has an Ordnance Survey trig point (a survey pillar).

The same 770 m appears in the Walking World route from Croesor, with Moelwyn Bach at 710 m.

go4awalk ranks it 43rd among the highest mountains in Wales.

Moelwyn Bach is 710 m and Craigysgafn, the rock peak between the two, is 689 m, both per go4awalk’s Tanygrisiau circuit.

Starting at Tanygrisiau

In The Great Outdoors, Emily Woodhouse’s route of 30 August 2023 is 6.5 miles (10.5 km). It has 750 m of ascent and takes 4 hours.

Its sequence from the start:

  1. Park at the small roadside car park south east of Tanygrisiau station, grid reference SH 685 448.
  2. Walk up Cwmorthin. The waterfall soon appears on the left, then Llyn Cwmorthin, the lake.
  3. Pass the ruin of Capel Rhosydd, an isolated chapel, and go through the Cwmorthin quarry ruins.
  4. Pass to the right of the flooded pit and continue up the incline (a steep old quarry track) to Rhosydd.
  5. Follow the footpath up a grass spur onto the summit.

The same guide says to look out for Snowdonia Slate Trail markers. It adds that the way becomes less obvious for a while, so head roughly south across the black landscape.

Other Tanygrisiau circuits give other figures:

  • go4awalk: a circuit over Moel-yr-hydd, Rhosydd Quarry, Moelwyn Mawr, Craigysgafn and Moelwyn Bach. It is 6.2 miles (10.5 km) with 820 m of ascent in 5 hours, Grade 6 (Moderate). It goes up by Moel-yr-hydd and comes down by Stwlan.
  • Mud and Routes: the Moelwyn Bach, Mawr and Cwmorthin circular is 12.43 km with 805 m of ascent. It goes the other way round, up by Llyn Stwlan and down through Cwmorthin, and gives no time.

go4awalk lists full mountain gear for its circuit: boots, warm layers, waterproofs, food and water, and good weather.

Mud and Routes warns that in anything but perfect conditions the Moelwynion can be highly challenging to navigate and keep your feet dry.

The Croesor start and the west ridge

Walking World calls Tanygrisiau the most popular approach, tracing the pathways and inclines of the old slate quarries.

Its western approach is quieter and less affected by the old quarrying. The paths are not as obvious as on the Tanygrisiau route, but navigation is simple enough.

Walking World Walk 6592 climbs the grassy west ridge. It is 5.6 miles with 756 m of height gain in 3 hours 31 minutes, graded Strenuous.

That walk takes in Moelwyn Mawr and Moelwyn Bach from Croesor. The ridge path is steep in places, but not excessively so. Some walkers may feel more secure using walking poles.

The other Croesor routes below go by the quarries, not by the west ridge:

  • Walking Britain 3035: The Moelwyns from Croesor, by Lou Johnson, goes by Croesor Quarry and Rhosydd. It is 7.5 miles (12.2 km) with 915 m of ascent in 6 hours 30 minutes, graded mod/hard.
  • Walking Britain 1422: Cnicht and Moelwyn Mawr from Croesor, by Peter Smyly. It is 8.0 miles (13 km) with 909 m of ascent in 6 hours 40 minutes, graded moderate.
  • go4awalk gw288: via Rhosydd Quarry, over Moel-yr-hydd, Moelwyn Mawr and Moelwyn Bach. It is 8.25 miles (13 km) with 926 m of ascent in 6 hours, Grade 6 (Moderate).
  • The Walking Englishman: Moelwyn Mawr from Croesor goes up the Croesor Quarry tramway. It is 6.3 miles (10.1 km) with 702 m of climbing in 3 to 4 hours, rated Hard.

Craigysgafn and Moelwyn Bach

Two small walkers on a steep rocky col between two summits.

Walking World crosses Craigysgafn, the intermediate rock peak, on the way to Moelwyn Bach.

It describes a steep descent where you may have to put away the walking poles to use your hands. Moelwyn Bach then follows on without any drama.

The other guides say this about the crossing:

  • Walking Britain 3035: Craigysgafn is a rocky minor summit and a delightful section, with opportunities for scrambling if desired. Moelwyn Bach is not as bad as it looks in ascent, despite a few loose sections.
  • The Walking Englishman: the Craigysgafn path down from Moelwyn Mawr was steep at times, meandering around rock bluffs.
  • Mud and Routes: Craigysgafn is good ridge walking, with glimpses down to Llyn Stwlan through the crags. From Bwlch Stwlan a clear and steep path leads up Moelwyn Bach.
  • walk-snowdonia: the descent south to Bwlch Stwlan is quite steep, onto the rockier Moelwyn Bach.

Quarry ground: stay on the paths

The Tanygrisiau routes above, and the Croesor routes by Rhosydd, all pass old slate workings.

Two walkers at the fenced entrance of an old slate mine tunnel.

Coflein is the record kept by the Royal Commission on the Ancient and Historical Monuments of Wales. It says Cwmorthin Slate Quarry was worked from about 1810 to 1939.

Its surface remains lie over a still more complex series of underground workings.

A major underground collapse in 1884 closed half the workings. Coflein says work ceased in 1939 and the quarry was sold in 1970.

The Daily Post gives a later end. It reports that the quarry closed in 1970 but small-scale working continued until 1997.

Coflein’s account of Rhosydd says the slate was found in the early 1830s but not worked seriously until 1852 or 1853. A huge rock fall in 1900 destroyed much of the eastern workings, and the mine was worked until 1930.

go4awalk says Rhosydd opened in 1840 and employed some 200 men. Coflein also records a 675 m adit (mine tunnel) driven at Level 9 between 1862 and 1871.

What the guides say about the workings:

  • go4awalk: since closing in 1930, the ruined buildings at Rhosydd have become dangerous and unstable. It is best to stay out of the buildings and tunnels.
  • Walking Britain 3035: on the way to Rhosydd, do be careful as there are many adits and unfenced chasms that could cause problems.
  • Walking Britain 1422: Moel yr Hydd is seen beyond unfenced quarries.
  • The Great Outdoors: many of the adits at Rhosydd are still open. It is advisable not to enter them without an experienced guide. Roof collapse and rock-fall are common, in its Rhosydd piece.
  • Mud and Routes: exploring any workings and entering any buildings is not recommended. Take care with any structure, because they are often unsafe.

In mist, Mud and Routes says to stick to the path. There are open quarry workings along the wide col east of the summit, where the fence towards Moel-yr-hydd is electric.

Its Rhosydd quarry walk adds that at Bwlch y Rhosydd, in mist, you need to take care that you can find the track back down.

On 24 August 2024 a walker fell about 100 ft (30 m) into an old mine shaft at Cwmorthin. The Daily Post reported the fall at the abandoned slate quarry near Tanygrisiau.

Parking and the way there

  • Tanygrisiau: The Great Outdoors describes a fairly small car park off the side of the road, just south east of the station, at SH 685 448. Mud and Routes, in a 2015 guide, calls the parking limited.
  • Bus and train: the same 2015 guide says Tanygrisiau has a bus service from Blaenau Ffestiniog. The Great Outdoors gives trains to Llandudno Junction, then a train to Blaenau Ffestiniog, and starts from the car park or railway station.
  • Croesor: Walking Britain 3035 names the National Park car park in Croesor, grid reference SH631446. It is the car park the Cnicht route uses.
  • Map: go4awalk lists OS Explorer OL18, Harlech, Porthmadog and Bala.

The Precipice Walk is a moderate walk with the Moelwynion to its north.

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