Trail Running > Routes > Brecon Beacons Routes > Fan Brycheiniog
A 21 km trail run on the wilder side of the Brecon Beacons offering rugged mountain beauty and tranquil lakes.
Why run this trail?
At 802 m, Fan Briechyniog is highest point in the Black Mountain range and the fourth highest in the Brecon Beacons overall. it’s a magnet for walkers, runners and even the occasional extreme thrill-seeker (more on that later). Yet this western fringe of the National Park – known as the Carmarthen Fans – feels a world apart from the tourist bustle of Pen y Fan.
There’s a stark beauty about these mountains. Think Wordsworth’s Grasmere rather than the picnic blanket spirit of Pen y Fan; a tankard of nut brown ale as opposed to a supersized fizzy soda. You get the idea. This is a wilder, more secluded side of the Brecon Beacons.
This route adds around 5 km to the classic Fan Brycheiniog Fell Race, taking in the summit of Picws Du before dropping to the serene water of Llyn y Fan Fach. The return leg skirts Llyn y Fan Fawr and traces the bottom of the valley back to the finish at Tafarn y Garreg.
The Climb to Fan Hir
I hit the trail at 8:30 am on a warm, cloudy July day that cast the landscape in muted tones – a morning for mood lighting rather than dazzling technicolour.
Crossing the River Tawe, I soon fell into step with two runners from Cardiff on a recce for an upcoming race. Together we puffed up the steep, winding climb through the bracken to Allt Fach, swapping a few words between gasps of air.
As the trail broadened onto open moor and the gradient eased, the dark sweep of Fan Hir came into view. At 761 m, this ridge is no minor feature – a graceful 3 km spine of rough grass and stone slabs, its eastern edge falling away in a dramatic line of sandstone edges.
Fan Hir and Fan Brycheiniog
The ridge was a delight to run – easy footing, sweeping views and plenty of oxygen compared to the fug of the initial climb. Halfway across, I encountered the first of many weary figures: stragglers on the Brecon Beacons 100-mile ultra. With 75 miles in his legs already, one runner was barely moving and glad of some interaction. I offered a sympathetic ear and a couple of Haribo. Wishing him luck and trying not to look too fresh, I peeled away to my second summit of the day.
From Fan Hir it’s a short dip and a brisk pull up to the trig point at Fan Brycheiniog. The summit panorama was stunning: the mirrored bowl of Llyn Fan Fawr below, the big Beacons to the east and even the faint outlines of the Cambrian Mountains to the north. Wisps of low cloud licked the mountain top around me and added to the atmosphere.
Fan Foel to Picws Du
An easy five-minute jog took me across to Fan Foel (781 m), where the first glimpses of the water at Llyn y Fan Fach appeared to my left, the jutting mass of Picws Du above it. The curving escarpment of Bannau Sir Gaer beyond – with its tiered wafers of rock – provided clear sight of my onward route. I paused to take in the remains of the Bronze Age burial mound on Fan Foel before pushing on.
Picws Du (749 m) is a steep green slab with a straight-up track. The 500 m climb from the stream at the bottom to the summit averages out at 20% – a real lung buster. I had flashbacks of climbing Cribyn on my Pen y Fan Horseshoe run a couple of days earlier. At the cairn on top I took a breather: the day’s last major climb was in the bag.
The Amphitheatre of Bannau Sir Gaer
The ridge of Bannau Sir Gaer curves like a natural amphitheater above Llyn y Fan Fach, its broad grassy back gradually easing downwards. All along the way, I passed more ultra-runners – walking wounded in various states of disrepair. One was curious: if I wasn’t doing this race and I wasn’t training for a different race, why was I here at all? An existential question, and one that I would have time to ponder over the miles that followed.
Near the end of the ridge I caught the eye of a tense looking climber laying out his hard hat and pack on a steep, grassy patch high above the lake. He looked a little shifty.
Descent to the Lakes
My route soon took me off onto a steep track that dropped 100 m of altitude in a matter of minutes to the water below. Suddenly, I was looking at a crystal clear reflection of the escarpment I had just traversed, mirrored immaculately on the still surface of the lake.
Then came a surprise. From high above came a rising cacophony of shouts. An accident? My eyes scanned the ridge, then tracked quickly down to catch a fleeting glimpse of a parachute disappearing behind a rise. The “climber” I’d noticed earlier had just base-jumped off the ridge. That’s one way to make sure you get your Sunday lunch on time… or not at all.
Leaving the lake behind, I headed out over the moor on occasionally boggy tracks that soon narrowed and hugged the base of Picws Du, towering above in puffs of cloud.
A winding single track cut into the hillside took me around the foot of Fan Foel before opening out to reveal Llyn y Fan Fawr – the bigger of the two lakes – nestled at the foot of Fan Brycheiniog.
Tracking the shoreline of the lake I observed its quiet beauty, the occasional lone bird circling high above reflected in its polished surface.
The Final Leg
With 5 km left, I headed south along the valley floor with the craggy line of Fan Hir above to guide me. The final descent dropped 400 m of altitude on fast, grassy terrain that turned rocky and technical once I hit the line of bracken on the lower slopes. A final push took me over the river and back to my starting point at Tafarn y Garreg.
Arriving back at the road, I was surprised to find that the pub hadn’t opened yet – I’d made faster work of my run than expected. The downside? That supersized bucket of fizzy soda I now so desperately craved would have to wait. You really can’t have it both ways.
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More trail running routes in the Brecon Beacons
Trail Running Routes in the Brecon Beacons
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.