Safety information
Welsh mountains demand respect. Conditions can change in minutes — even Snowdon in July sees casualties from inadequate kit and unexpected weather.
Carry: waterproofs, walking boots, warm layer, hat & gloves, OS Explorer OL17 (Snowdonia) or OL18 (Harlech & Bala), 1.5 L water, charged phone, head torch. Check the weather at mwis.org.uk on the morning. In an emergency call 999, ask for Police / Mountain Rescue, give your what3words location. Local team: the relevant Mountain Rescue Team.
At a glance
The higher Moelwyn summit (770 m / 2,526 ft) above Blaenau Ffestiniog — a volcanic ridge with outstanding 360-degree views: Snowdon to the north, Cardigan Bay to the west, and the extraordinary grey-slate quarry landscape of Blaenau Ffestiniog directly below. Classic approach from Croesor (4 miles return) or Tanygrisiau (Ffestiniog Railway request stop). 4–6 hours. LL41 3PF.
About Moelwyn Mawr
Moelwyn Mawr (770 m / 2,526 ft) is the higher of the two Moelwyn summits — a volcanic mountain ridge above the narrow pass separating the Glaslyn valley system from Blaenau Ffestiniog in southern Snowdonia. Less visited than the more famous peaks of the Snowdon and Glyderau groups, the Moelwyns offer a 360-degree summit panorama that takes in Snowdon, Cadair Idris, Cardigan Bay, and most distinctively, the extraordinary grey-slate quarry landscape of Blaenau Ffestiniog directly below — the vast terraced quarry holes, waste tips, and roofscapes of the former slate capital of the world, a landscape visible from no other summit quite so clearly.
The classic approach from Croesor (a remote hamlet in Cwm Croesor to the west, accessible by narrow road from Garreg) takes 4–6 hours return and is the most scenic route. Alternatively, Tanygrisiau (a request stop on the Ffestiniog Railway) gives an eastern approach through the quarry landscape — making a car-free combination of heritage railway and mountain walking genuinely achievable. The Moelwyns traverse (Moelwyn Mawr → Moelwyn Bach) extends the day by about 2 miles.
Find it on the map
Frequently asked questions
Moelwyn Mawr's position — above the narrow pass that separates the Glaslyn valley system from Blaenau Ffestiniog — gives it a distinctive 360-degree panorama. To the north: Snowdon (1,085 m), the Glyderau, and the Carneddau fill the skyline. To the north-west: the Nantlle Ridge and the Llŷn Peninsula beyond. To the west: Cardigan Bay and, in clear conditions, the Irish coast. To the south: Cadair Idris and the Rhinogydd. Directly below, to the east: the extraordinary grey-slate landscape of Blaenau Ffestiniog — the waste tips, quarry holes, and slate roofs of the former slate capital of the world — a landscape unlike anything else visible from a Snowdonia summit. The combination of natural mountain scenery and industrial archaeology below makes the view from Moelwyn Mawr uniquely compelling.
There are three main approaches to Moelwyn Mawr. From Croesor (a small hamlet west of Blaenau Ffestiniog, LL48 6ST): the standard western approach, following a track and path up Cwm Croesor and then onto the south-west ridge — approximately 4 miles and 650 metres of ascent. From Tanygrisiau (below the Ffestiniog Railway Tanygrisiau reservoir): the eastern approach, climbing through the quarry landscape above the village — shorter in distance but through more industrial terrain, with the reservoir of Llyn Stwlan above. From Blaenau Ffestiniog itself: a longer approach through the quarry areas, less clearly marked. The Croesor approach is the most scenic; the Tanygrisiau approach is useful for visitors arriving by Ffestiniog Railway (Tanygrisiau is a request stop). The summit ridge connects Moelwyn Mawr to Moelwyn Bach (770 m → Croesor Quarry → Moelwyn Bach at 710 m) for a traverse.
The Moelwyn mountains are inseparable from the slate industry that defined Blaenau Ffestiniog — the flanks of the mountains are honeycombed with the adits (horizontal mine tunnels), open quarry faces, and waste tips of the Oakeley, Llechwedd, and Maenofferen slate quarries. From the summit of Moelwyn Mawr, the extraordinary extent of slate extraction is visible: the great terraced quarry holes, the grey-blue tips that form the town's backdrop, and the routes of the narrow-gauge tramways that carried slate down to the Ffestiniog Railway at Blaenau. Llyn Stwlan, the reservoir above Tanygrisiau, was built to power the Ffestiniog Power Station — a pumped-storage hydro-electric scheme using the height difference between the reservoir and Llyn Trawsfynydd below. The slate quarry adits were used during World War II to store over 2,000 artworks from the National Gallery in London — removed to safety from the risk of bombing.
Yes — the Ffestiniog Railway, which runs between Porthmadog and Blaenau Ffestiniog through the heart of Snowdonia, has a request stop at Tanygrisiau (the penultimate station before Blaenau Ffestiniog, on the eastern approach to the Moelwyns). From Tanygrisiau station, it is possible to ascend to Moelwyn Mawr via the Tanygrisiau reservoir approach — a route of approximately 3 miles and 600 metres of ascent. Blaenau Ffestiniog station (both Ffestiniog Railway terminus and Conwy Valley Railway station) is 2 miles from the mountain and also forms a viable base. The combination of a Ffestiniog Railway journey (55 minutes from Porthmadog, through magnificent mountain scenery) with a walk up Moelwyn Mawr makes for an excellent car-free day in this part of Snowdonia — a genuinely unusual itinerary combining heritage railway and mountain walking.
Croesor (Cwm Croesor) is a small, remote hamlet at the head of a narrow glacial valley west of Blaenau Ffestiniog, accessible by a narrow road from Garreg near Penrhyndeudraeth. The valley is enclosed by the Moelwyns to the east and the Cnicht ridge to the north — sometimes described as the "Matterhorn of Wales" for its pointed profile when seen from the south-west, though Cnicht (689 m) is not especially difficult. Croesor hamlet has a small car park and is the classic western starting point for Moelwyn Mawr. The Croesor Quarry (an important slate quarry, now closed) is visible on the hillside above the hamlet, and the valley retains a profoundly peaceful, unspoilt character — one of the least-visited accessible valleys in Snowdonia. Cwm Croesor is a good base for a day walking the Moelwyns without the need to go through Blaenau Ffestiniog.