Carnedd y Filiast and Arenig Fach (Welsh Marilyn)

A tough mountain day on rarely climbed hills combining the pleasantly easy Marilyn of Carnedd y Filiast with the beastly difficult Marilyn of Arenig Fach via the most notorious bog in North Wales.


7 May 2023

No dogs allowed

From the layby at the Memorial Chapel, we head back east along the road to begin the ascent of Carnedd y Filiast on an excellent track that climbs steadily and easily all the way to the summit and our first Marilyn of the day. There are excellent views across the Migneint to the Snowdonia peaks and south across Llyn Celyn to Arenig Fawr.
Party (well, coffee!) over and the bog fest begins. A squelchy runnel poses as a path westwards beside a fence with irksome deviations to cross innumerable water courses. Some solid ground provides a temporary respite over Carnedd Llechwydd-llyfn before a boggy descent to the more substantial barrier of the Afon Gelyn. [Note if the Afon Gelyn is in spate, we will not be able to cross and footsteps will have to be re-squelched back to SH843442 and the bridleway followed down to the road leaving Arenig Fach for another day].

Assuming the river can be crossed, with or without dry feet, 1.5km of pathless, rough ground follows to gain the foot of the NE ridge of Arenig Fach and a view of Llyn Arenig Fach. This section is a little less arduous than might be expected as deep heather is mostly avoidable and there is even the occasional sheep track heading fortuitously in the right direction. Sprits rise at the start of the steep ridge as a path appears beside the fence. However, it soon vanishes and an exhausting, struggle up steep heather and tussocks of vegetation is required to gain the summit of Arenig Fach. The top sports a Bronze Age funerary cairn (Carnedd y Bachgen) along with a wind shelter, large cairn and trig point.

The relief of firm ground is short lived as the descent SSE towards Y Foel soon degenerates into deep heather hiding rocks and holes. After losing 100m of height we head E then NE to regain the fence line coming down steeply from the top where a prominent stile has attracted enough traffic to form a path (yes, a path!). Crossing the stile, the path, at first intermittent and then more distinct is followed down to the edge of the access land. Maes-y-tail is skirted to pick up a right of way that runs parallel to the road to join it just before it crosses the Afon Geylyn. Never has tarmac been a more welcome sight and it is a short walk along the verge back to the cars.

Large sections of pathless, rough terrain, tussocks and heather steep in places. Long boggy sections. Tracks, occasional paths, river. Good waterproof boots, gaiters and poles essential. A spare pair of socks might be welcome in case of wet feet crossing the Afon Gelyn.
OL18 Harlech, Porthmadog and Bala
Starting Point:
Capel Celyn (Memorial Chapel) layby on the A4212 at the western end of Llyn Celyn. Note, if full there is a larger layby a short distance back E GR SH848414 Postcode LL23 7NY
Walk Starts:
Walk Finishes:
Highest Point:
689m Arenig Fach


Let the walk leader know of any relevant medical conditions

Refer to the Handbook for walk related information and specifically for recommended walking equipment and safety information

Remember you are responsible for being properly equipped

Ensure you have the walk leader’s phone number in case of an emergency

If you become detached from the group STOP, call out; try contacting group by phone or text. If no contact return to the last place you were with the group. Wait 30 mins repeatedly trying to make contact. After 30 mins seek help and/or make your own way safely.

The Google map below is the location of the walk start point.