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About this place
Llyn y Fan Fawr is a glacial lake in Powys, Wales, on the western side of Bannau Brycheiniog (Brecon Beacons) National Park. It sits directly beneath Fan Brycheiniog, the high point of the Black Mountain range, also known as the Carmarthen Fans.
What is it?
The Welsh name translates roughly as "lake of the big peak". Ice carved the basin during the last glaciation, leaving a dark pool under a steep escarpment. It ranks among the biggest glacial lakes in South Wales, and the surrounding country is wilder and quieter than the busy Pen y Fan area.
Is it the same as Llyn y Fan Fach?
No. Over the ridge lies a second lake, Llyn y Fan Fach ("lake of the small peak"), home of the Lady of the Lake legend. Walkers often join the two into one loop, but they are separate places with their own approaches.
How do you get there?
Only footpaths lead to the water. One popular route starts from the Trecastle road near Maen Mawr: a loop of about 8 km, roughly 3.5 hours, with around 400 m of climbing. A longer circuit of about 15 km and 4.5 hours takes in both lakes. Use OS Explorer map OL12. Access roads can become difficult or impassable in snow and ice.
What will you see?
From the shore you look across dark water to a sheer slope. The toughest stretch is the climb from the lake to the saddle at Bwlch Giedd, where the path has steps eroded in places. Turn right at the saddle for Fan Brycheiniog, 802 m above sea level, with a trig pillar and a shelter. Views reach the Central Beacons and Pen y Fan, the Black Mountains and the Epynt range to the north. A short detour to Fan Foel gives a look down on Llyn y Fan Fach.
When should you go?
Late spring to autumn on a clear day gives the best visibility. After rain the route turns very boggy, so waterproof boots help. In winter the exposed ridge loses visibility quickly and calls for experience and proper kit.
Frequently asked questions
Can I reach the lake without climbing the summit?
Yes. The lake is a shorter objective on its own; Fan Brycheiniog is a steep extension.
How high is Fan Brycheiniog?
About 802 m, the highest point of the Black Mountain range.
Is Llyn y Fan Fawr the lake from the Lady of the Lake legend?
No, that story belongs to Llyn y Fan Fach, a different lake on the other side of the ridge.
Is the walk hard?
Moderate. Expect a steep climb, wet ground and exposed terrain where navigation matters.
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