Trail Running > Routes > Snowdonia Routes > Yr Eifl & Tre’r Cairi
A dramatic 10 km mountain run over Yr Eifl, combining technical trails, Iron Age history and panoramic coastal views.
Why run this trail?
The trio of peaks known collectively as Yr Eifl – often anglicised as “The Rivals” – are among the most distinctive mountains in Wales. Rising abruptly from the turquoise waters of Caernarfon Bay, their isolated position on the northern edge of the Llŷn Peninsula creates a dramatic landscape that feels entirely separate from the rest of Eryri.
They make an excellent fell-running circuit and are a particularly good option when cloud and rain engulf the higher peaks of Snowdonia. The Llŷn Peninsula enjoys a noticeably drier microclimate, and the views from Yr Eifl frequently extend far beyond the mountains to encompass Anglesey, the distant coastline of Cardigan Bay and even the Isle of Man and the Cumbrian peaks on very clear days.
Although the highest summit reaches a modest 564 m, every metre of ascent feels earned when you’re climbing directly from near sea level. Steep gradients, sprawling boulder fields and some technical descents add plenty of challenges, while the constant backdrop of coast and mountains makes this one of the most memorable short trail runs in North Wales.
Car Park to Garn Fôr
The run sets out from the large car park situated at the top of the switchback road down to the historic village of Nant Gwrtheyrn. Cross directly onto the moor opposite to pick up the gravel 4×4 track that bisects the lower slopes of Yr Eifl and heads off diagonally to the left up the hill.
It’s the perfect warm-up gradient on an easy surface, meaning you can focus on the amazing views down to the coast on your left: the lush cliff faces and sweep of sand beyond the village lapped by a huge expanse of blue ocean. To your right, the peak of Garn Ganol – the highest summit in the range and generally referred to as ‘Yr Eifl’ – dominates and looks loftier than its advertised height.
The track soon kinks away from the coast slightly and you’ll arrive at a bwlch between the slopes of Garn Fôr and Garn Ganol.
Garn Fôr is the smallest and most northerly of the range, its heavily quarried tiers resembling a wedding cake silhouetted against the sea. Access to this hill is effectively restricted – the area is fenced off and entry is discouraged for safety reasons.
Garn Fôr to Lôn Yr Eifl
Continue over the crest of the bwlch and the track begins to descend, with great views of the coastline and the impressive hills of Gyrn Ddu, Gyrn Goch and Bwlch Mawr ahead.
The gravel track now becomes a grassy path across the moor and drops quickly towards the village of Trefor. Just before you reach some farm buildings, look out for a discreet rusty iron gate, set into the drystone wall to your right.
Pass through the gate into a magical little cwm, thick with bracken and dotted with small trees – the path is indistinct, overgrown and obviously hardly used. You’ll soon ford a stream under the large crags of the northern slopes of Garn Ganol before the path undulates through a series of fields and broken stone walls to reach a small lane – Lôn Yr Eifl.
Lôn Yr Eifl to B4417
Turn right on the lane and follow it as it winds around a scenic valley. After 700 m, pass through the gate on the right hand side of the lane, just opposite the entrance to a farm (Merbwll Uchaf). The path onto the hillside is a little faint here, but go straight up the steep bank ahead.
Follow the red-topped footpath posts across several fields. These are a little patchy at first, but soon become more frequent and easy to follow. You’ll shortly emerge onto the B4417.
B4417 to Tre’r Ceiri
Turn right and head uphill carefully on the road for 350 m. If you glance over your right shoulder, you can’t miss the scree-topped mound of Tre’r Ceiri – your next destination on this route.
Look out for a fingerpost on your right set back from the road above a broken stone wall. Head up the bank and pass through the gate onto the hillside.
The climb up to Tre’r Ceiri begins fairly innocuously, quickly starts to nag, then turns into a grind up some very large rocks. At least it’s easy to navigate – in fact, there are so many paths through the heather towards the top that you could probably never ascend via the same route twice.
The gradient averages out at about 20% over the kilometre or so of distance to reach the top of the mountain, so it’s an honest climb by any measure.
The top of Tre’r Ceiri is one of the most perfectly preserved Iron Age hill forts in Europe – a huge expanse of about 160 stone hut circles and surrounding ramparts that look incredibly intact considering the exposure to the elements they have withstood for over 2,000 years. The summit cairn stands at 485 m and offers a fantastic 360-degree panorama due to the mountain’s isolated aspect.
Once you’ve done a loop of the fort, follow the clear exit path between walls – which may have originally been the main fort entrance – to descend into the saddle between Tre’r Ceiri and Garn Ganol.
Tre’r Ceiri to Garn Ganol (Yr Eifl)
With most of the ascent having been done to get to the top of Tre’r Ceiri, the final push to Yr Eifl is only about another 150 m of vertical gain, but every one of those metres provides a test of some sort.
The track is narrow, steep and winds through some huge boulders that require a bit of hands-on in a couple of places. It’s not the most fluid of running, but it’s exhilarating and feels like you’re scaling a much bigger mountain by virtue of the incredible views as you climb.
Once you scramble out on the rocky summit of Yr Eifl the payoff is clear: stunning views in every direction and a proper mountain high in every sense of the word. On a practical note, it’s worth bringing an extra layer as the top is very exposed due to its proximity to the coast and isolated position.
Garn Ganol (Yr Eifl) to Car Park
This route takes the southern path to descend from the summit. It’s a steep, twisting, rocky and exciting drop that will test those descending skills to the max. Some of the track is cut into deep, narrow channels of moorland so there’s absolutely no escaping the obstacles either. Absolutely perfect!
The gradient eases about two-thirds of the way down and it’s a fast home run on welcomingly soft grass back to the car park.
On reflection, it’s remarkable just how much variety is packed into such a compact circuit – coast, mountain, ancient history and some properly technical terrain all condensed into a mere ninety minutes of running these truly memorable hills.
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Disclaimer
All routes and GPX files are provided as a guide only. Conditions, rights of way, and landmarks may change. Always carry an up‑to‑date map and use your own judgement. See the Trail Run Disclaimer page for details.