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Carnedd y Filiast – Under the Slabs

By Dave Roberts   

on September 7, 2014    5/5 (1)

Carnedd y Filiast – Under the Slabs

Route Essentials

Route Summary

See the end of the article for local information about parking, public transport facilities, pubs and cafes.


12.65 km


602 m


Calculate the time using Naismith’s Rule and factor in your own pace.

Start Location



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Remember that we cannot outline every single hazard on a walk – it’s up to you to be safe and competent. Read up on Mountain Safety , Navigation and what equipment you’ll need. 

Carnedd y Filiast – Under the Slabs Ordnance Survey Map and GPX File Download

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Carnedd y Filiast – Under the Slabs

This is a route up Carnedd y Filiast from Deiniolen, but with an interesting return down through Cwm Perfedd and Cwm Graianog. Would make a much better route starting from Nant Ffrancon.

1 The route starts at the road head at Marchllyn, with an easy and steady walk up the reservoir road as far as the last bend (SH615 624) around 2.25km, where you turn left instead.


2 Follow the track as it curves around for 100m or so, and then take the obvious path to your right uphill, past the stile as there’s a huge gap in the fence. This path takes you up to the bwlch below Carnedd y Filiast.


3 Today I walked to the minor 721m top to the left.Otherwise, continue to the small tarn in the bwlch and head right up the slope. This path can be tricky to find in mist, even if you know where it is, so best of luck. One option is to walk to the corrie lip and follow that up. It also seems that someone has blazed / vandalized this path recently with red paint (although someone mentioned it could be a race and the paint might be temporary?) so at least it’s currently easy to follow once you get to the top of the slope.

Elidir Fawr
Elidir Fawr


4 The path reaches a more difficult section ahead (ring contour on the map) where you turn right – as per the helpful arrow – and contour along to the summit. This is bouldery, and can be avoided by taking a path around the left of the hill towards a grassy area and ascending from that side.

Carnedd_y_Filiast -4483

5 Enjoy the view!

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6 You continue along the grassy ridge, towards a stone wall and a stile. This is where the new blazes end. Veer left to walk along the corrie lip (if visibility allows!) and you get to see the impressive slabs. You’ll be walking in Cwm Graianog far below soon enough!

Carnedd_y_Filiast -4503

7 Continue on the ridge to Mynydd Perfedd, which has no discernible re-ascent on the ground, cross the fence and descend the clear path to Bwlch y Brecan. This is where the old track that crosses from Cwm Dudodun to Nant Ffrancon used to be, and the initial section of track is excellent (relatively speaking!)

DSC_0816 8 – Follow the path, which is even slabbed in places, downhill towars the obvious ridge shown in the photo above. You can even make out the path, which begins to peter out as you reach the end.

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9 – You’re now off path, and you can turn south into Cwm Bual and contour around to Cwm Idwal, or take the less trodden route north. Although, everyone I passed on the summits seemed to be going in the same direction! The views are stupendous, unexpected and largely unfamiliar as they’ve only been seen from above or below in the past. Foel-goch’s northern crags dominate that direction, and was unfortunately in shade this afternoon. A photograph for an evening walk for certain.

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10 – From the end of the ridge – marked Y Galan on the map – I followed an earthwork down the slope and towards the sheepfold marked on the map.

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11 The going gets no easier as you contour around and probably gain some ground in order to enter Cwm Graianog. The Carnedd y Filast slabs fill the skyline, with the SE Ridge to your left looking more like the summit. The group ahead of me had scrambled down this ridge. It’s a majestic view that I was fortunate enough to capture – even shooting into the sun.

Carnedd_y_Filiast -4533

12 Cwm Graeanog seems to have the remains of a moraine that was just never watertight enough to hold a corrie lake, and this forms a natural and steady descent for a distance, before you head on directly downhill.

Carnedd_y_Filiast -4537
13 The route’s a bit steep from here onwards, and you’ll need some grippy boots to stay on your feet. You’ll need to plod on between the bracken, making the most of any rocks to aid your traction, and thankfully hasn’t got any tricky bouldery sections.. It’s only 150m descent, and while it may be steep, it’s over soon enough.


14 You can either walk over to Bethesda (left) along the Lon Las Ogwen, or right up towards Idwal Cottage. A Much better version of this route would be to start off up Cwm Ceunant to climb Filiast from this end in order to walk a compact horseshoe.


Local Information and Recommended Maps and Guidebooks

Route Summary:

This walk includes the Washi of Carnedd y Filiast (Glyderau)

This walk includes the Hewitt of Carnedd y Filiast (Glyderau)

This walk includes the Nuttall of Carnedd y Filiast (Glyderau)

Route Start Location:

12.65 km 602 m

Calculate the time using Naismith’s Rule and factor in your own pace.

Activivity Type: 

Summits and Places on this Route


Check out the businesses nearby for more places to stay and drink.


Remember that we cannot outline every single hazard on a walk – it’s up to you to be safe and competent. Read up on Mountain Safety , Navigation and what equipment you’ll need.

Parking :

Public Transport:

Traveline for UK Public Transport

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Dave Roberts

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