Stwlan Dam, Moelwyn Mawr & Rhosydd Quarry

The winding road that leads down from Stwlan Dam to Blaenau Ffestiniog and Tanygrissau.

A unique days hike from just outside Blaenau Ffestiniog with stunning views across Snowdonia, the winding road from Stwlan Dam and quarry ruins at Rhosydd.

  • Dawn
  • Daytime
Route Facts
  • 8km
  • 454m ascent, optional extra 200m to take in two peaks
Best For
  • Dawn across Llyn Cwmorthin
  • Views down the road from Stwlan Dam into Blaenau.

The route

We start at the small town of Tanygrissau at the cafe carpark just along from the station. The route then climbs up the old quarry tracks in three stages to reach Stwlan Dam. We’ll stop here for a photo break taking in the winding road and hoping for a view of cyclists you often get up here. The route then climbs up the left hand side of Llyn Stwlan to the shoulder of the two hills where we get views down to the coast. From here we can either take the high route taking in the peaks of Craigysgafn (689m) and Moelwyn Mawr (770m) or for those prefering the easier route we cross the slag heaps behind Llyn Stwlan.

Both routes options eventually meet at the ruins of Rhosydd Quarry which contains many old slate quarry buildings. Finally we descend the valley to Llyn Cwmorthin and then follow the roads back into Tanygrissau.

I find this route is best started in the morning arriving at Stwlan Dam just before lunch. If you’re looking for a Dawn or Sunset walk it’s best to walk the route in reverse to get the best use of the light unless you want to get up high for the sunrise in which case we walk a large proportion of the route in the dark.


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