Cwmorthin Valley & Rhosydd Quarry Walk
Follow a short but spine-tingling walk from the village of Tanygrisiau up into the hidden glacial valley of Cwmorthin, where a ruined chapel, roofless quarrymen's cottages and a steel-grey mountain lake sit in almost eerie silence. It is one of the most atmospheric hidden-gem hikes in all of Snowdonia.
The Walk Itself
The trail begins at Dolrhedyn above Tanygrisiau and quickly delivers you to the ruins of Cwmorthin Quarry, Plas Cwmorthin and Rhosydd Chapel — the bones of a community that once thrived here. Follow the shoreline of Cwmorthin Lake towards the valley head, where the path steepens dramatically up a rocky incline towards Rhosydd Quarry.
At Rhosydd the ruins of an old mill are still standing, and the sense of industrial abandonment against the raw mountain backdrop is genuinely striking. On a clear day, the route can be extended along ridgeline paths towards the summits of the Moelwynion.
The Moelwyn Mountains
Moelwyn Mawr and Moelwyn Bach are the two main peaks of the Moelwynion range that towers over Blaenau. They are among the least-explored mountains in Snowdonia, which means you are unlikely to share the summit with a crowd. On a clear day the reward is superlative: sweeping views across Cardigan Bay, the Llŷn Peninsula coast and the Harlech Dome.
The name Moelwyn means 'bald white hill' — and the two peaks are quite different in character, Mawr being the broader, more rounded summit and Bach a sharper, rockier proposition. Both are accessible via Cwmorthin as a base.
When to Go
The Cwmorthin walk is impressive in all weathers — low cloud and mist give the ruins a gothic, otherworldly quality, while sunshine turns the lake a brilliant steel-blue. It is a genuine year-round route, though the incline to Rhosydd becomes slippery after heavy rain, so trekking poles are advisable.
Start early to have the valley to yourself. The walk to the lake and back is manageable in under two hours; adding the Rhosydd Quarry climb makes it a solid three-hour half-day.
Cwmorthin Valley & Rhosydd Quarry Walk on video
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