Moelwyn Mawr

Moelwyn Mawr

Overview

Moelwyn Mawr is a 770 m mountain in the Moelwynion of Eryri, between Croesor and Tanygrisiau. Its grassy slopes, rocky connecting ridges and extensive slate-quarry remains offer varied mountain circuits. The highest ground is beside the summit trig point. Routes with Moelwyn Bach, Craigysgafn or Cnicht require fitness, confident navigation and care on steep ground.

Summit and views

The 770 m summit is the ground beside the trig point at SH 65825 44864. The trig pillar is a useful landmark. Moelwyn Mawr North Ridge Top is a separate, lower rocky top at 649.7 m; it is not the main summit. In clear weather there are views across Cwm Croesor to Cnicht, towards Yr Wyddfa and the northern Eryri mountains, and west to the coast. The connecting ridges overlook Llyn Stwlan and its dam.

Walking routes

Croesor circuit via the west ridge, Craigysgafn and Moelwyn Bach

From Croesor village car park (SH 632 447), take the southern lane and uphill track onto Moelwyn Mawr’s west ridge. Follow the ridge to the summit, then leave east and turn south on the path through rocky ground to the col below Craigysgafn. Cross Craigysgafn with short hands-on sections and descend to Bwlch Stwlan. Take the slanting path across scree to Moelwyn Bach, avoiding its steep northern crag. Descend Bach’s west ridge to the plantation edge and lane, turning right back to the same car park. Welsh Country gives approximately 9 km and 4–5 hours for this full circuit. Steep, exposed sections need care in wind or wet conditions.

Tanygrisiau circuit via Cwmorthin, Rhosydd and both Moelwyns

Start at the small roadside car park southeast of Tanygrisiau station (SH 685 448). Follow the road past the designated railway crossing, then climb the track by Cwmorthin waterfall to Llyn Cwmorthin. Continue beside the lake and chapel ruins to Rhosydd’s surface quarry paths. Ascend the grassy spur to Moelwyn Mawr. Descend southeast and south via the Craigysgafn ridge to Bwlch Stwlan, then make the return excursion to Moelwyn Bach on its slanting scree path. Back at the col, take the reservoir-side path and cross the boggy basin below Stwlan dam, including a stream crossing, to reach the dam access road. Follow it downhill and retrace the initial road to the car park. This version includes the Bach excursion; allow time for both summits. Keep away from open workings and do not cross the dam or enter restricted plant areas.

Croesor horseshoe over Moelwyn Bach, Moelwyn Mawr and Cnicht

From Croesor car park, follow the southern lane to the plantation, then cross the moor and climb Moelwyn Bach’s western ridge. Descend on the slanting scree path to Bwlch Stwlan, avoiding the crag directly towards Moelwyn Mawr. Scramble over Craigysgafn and climb Moelwyn Mawr. Return briefly along the ascent path, then take the grassy spur towards Rhosydd Quarry, using surface paths between the workings. Continue across the boggy plateau towards Llyn yr Adar and join Cnicht’s northeast ridge. Climb Cnicht, then descend its southwest ridge and follow the lower track through the woodland to the original Croesor car park. Mud and Routes gives 15.38 km and about 6 hours for this full circuit. Rough route-finding and several steep rocky sections make this a demanding day.

Croesor west-ridge circuit returning by the southern quarry path

Start and finish at Croesor village car park (SH 6314 4468). Follow the southern lane, uphill track and stile to Moelwyn Mawr’s west ridge and climb to the summit. Take the southeast-then-south summit exit towards the col below Craigysgafn. Before climbing Craigysgafn, turn west down the southern quarry path to the ruined slate mill. Follow the old level around the hillside to the pulley-tower remains, rejoining the ascent path and lane to Croesor. This circuit omits both Craigysgafn’s summit and Moelwyn Bach. Explore Wild Wales gives approximately 8 km and 3 hours for this route. The upper ridge has steep northern drops, and quarry ruins and openings must be avoided.

Terrain and safety

Grassy mountain ridges, rocky paths and short scrambling sections, loose scree, boggy moorland, slate-quarry tracks, steep slopes and surfaced dam access road on the Tanygrisiau return.

• Steep crags border the summit and ridges. Craigysgafn has short scrambling sections; Moelwyn Bach’s northern crag cannot be descended directly towards Moelwyn Mawr. Use the slanting scree path to Bwlch Stwlan.
• Croesor, Rhosydd and other old workings contain open pits, shafts, unstable buildings and loose slate. Stay on surface walking paths, well back from openings. Do not enter mine tunnels or use the underground Croesor–Rhosydd through-trip as a walking route.
• Bog, wet grass, loose scree and slippery rock slow progress. The Tanygrisiau reservoir-basin return includes pathless wet ground and a stream crossing that may be unsafe after rain.
• Cloud can hide summit exits and the faint paths between Rhosydd and Cnicht. Carry a map and compass and know how to use them; a downloaded phone map alone is not enough.
• Llyn Stwlan and Tanygrisiau Reservoir are working pumped-storage waters. Keep out of the water and away from plant, intakes and restricted dam areas; follow signs and any temporary access restrictions.
• The Ffestiniog Railway is operational. Cross only at designated crossings, obey signals and signs, and never walk along the track as a shortcut.
• Exposed ridges are serious in strong wind, ice or snow. Check the mountain forecast, carry warm waterproof layers and a headtorch, and leave enough daylight for the entire return.

Rain makes slate, grass and scree slippery and can deepen bog or raise the stream below Stwlan dam. Wind and low cloud make ridge crossings and summit exits harder. Snow and ice require winter mountain skills and suitable equipment; short winter days need a conservative plan.

Access and facilities

Use the designated village car park in Croesor, around SH 632 447, for western routes. The Tanygrisiau quarry circuit described here starts at the small roadside car park southeast of the railway station, SH 685 448. The station also has a rough gravel parking area. These are distinct starts; check signs, charges and permitted use when you arrive. Keep lanes, gates and access for residents and emergency vehicles clear.

G25 buses link Blaenau Ffestiniog station with Tanygrisiau; check Traveline Cymru for current days and return journeys. Tanygrisiau is a Ffestiniog Railway request stop only on Mountain Spirit and The Quarryman services in the 2026 timetable. Confirm the operator’s calendar, stopping arrangements and last return before relying on it. Arrange travel to and from Croesor separately.

Tanygrisiau station has a small shelter but no other facilities, according to the railway operator. The Slate Trail lists the Lakeside Café at Tanygrisiau and a café in Croesor; check opening times rather than depending on them after a mountain walk. Carry food, drinking water, warm layers and waterproofs for the full outing. Keep dogs on leads around livestock and follow local access signs.

Geology

The Moelwyn landscape contains sedimentary rocks, volcanic rocks and igneous intrusions. The British Geological Survey describes contrasting resistant volcanic and softer sedimentary rocks shaping the glacially eroded skyline between Moelwyn Mawr and Yr Arddu. Ice carved the surrounding cwms and valleys. Boulder ridges extending into Cwm Croesor have been interpreted as a fossil rock glacier, although their origin is debated.

Name and history

Moelwyn Mawr is commonly rendered as “great white hill”: moel means hill or mountain, gwyn means white, and mawr means large. The reason for the colour reference is uncertain. Slate quarrying shaped the settlements and paths around the mountain. Croesor developed as a quarry village in the 19th century, and surviving inclines, barracks and slate tips mark the industry. The Croesor Tramway carried slate towards Porthmadog. Llyn Stwlan and the lower Tanygrisiau Reservoir later became part of the Ffestiniog pumped-storage scheme, commissioned in 1963.

Nearby landscape

Llyn Stwlan and its dam lie below the eastern slopes. Cwm Croesor is to the north and west; Rhosydd Quarry, Llyn Cwmorthin and old slate workings lie along eastern and northern approaches. Craigysgafn and Bwlch Stwlan link the two Moelwyn summits.