Arenig Fawr

Arenig Fawr

Arenig Fawr rises to 854 m (2,802 ft) west of Bala in Eryri (Snowdonia). It is the highest mountain of the Arenig group, with 480 m prominence. Its rocky crest stands above open moorland and Llyn Arenig Fawr, with far-reaching mountain views when cloud clears.

Which summit?

The main summit is the trig point at SH827369. The stone shelter and memorial are beside it. Arenig Fawr South Top (837 m) and South Ridge Top (714 m) are lower, separate tops on the southern ridge. Arenig Fach (688.8 m) is a different mountain to the north; Moel Llyfnant (750.1 m) lies to the south-west and is an optional extra summit on a longer day.

Choose a complete itinerary

The five route entries describe different full-return walks, not interchangeable ascent distances:

• Lake and Y Castell out-and-back: 10Adventures gives 10.1 km and 3.5–5 hours. This returns by the ascent line from the minor-road trailhead.
• Arenig with a northeast-ridge descent variant: Walking Britain gives 13 km and 5 hours 50 minutes, including the road approach from SH831392.
• Llyn Celyn and south-ridge circuit: The Great Outdoors gives 16.5 km and 5.5 hours from SH845403, returning by Amnodd-wen without climbing Moel Llyfnant. It includes A4212 verge walking.
• Arenig Fawr with Moel Llyfnant: Mud and Routes gives 17.1 km and 6 hours for its circuit from SH845395, returning via Amnodd Bwll and the former railway. The alternative Amnodd-wen return is a different line.
• Simdde Ddu Catwalk: Mud and Routes' 2011 guide describes an experienced-walker circuit from SH830392, returning via the bothy. Its narrative estimates about 12.5 km and 4 hours, while the header says 12.32 km. The airy cliff-side section and rough, partly pathless approach make this a distinct and more serious choice.

Terrain and decisions on the hill

The lake approach leads to Y Castell and a traversing path across the southeastern flank. Some tracks and paths are clear, but others fade among bog, rock and scree. A northeast descent must avoid crags; the southern circuit and the col towards Moel Llyfnant need careful navigation.

At the reservoir outflow, published guides describe different makeshift crossings. Assess the actual crossing and water level instead of expecting a dependable bridge. Wind and low cloud increase the difficulty of finding a safe line; snow or ice changes the character of the rocky upper ground. On Simdde Ddu, loose boulders can be hidden by heather and the cliff-side path is airy. Turn back if conditions exceed your experience.

Access, parking and the bothy

Llyn Arenig Fawr is the smaller reservoir below the eastern slopes. Llyn Celyn is a separate reservoir to the north. The parking areas and starts at SH831392, SH845395 and SH845403 serve different itineraries. Check local signs and leave gates and working access clear.

The MBA bothy beside Llyn Arenig Fawr is a tiny shelter, with space for two people, three at most. Do not plan around guaranteed overnight space. There is no local fuel, outside fires and vehicle access are prohibited, and sheep graze nearby. The MBA page has conflicting dog labels, so confirm its rules before bringing a dog inside. Consult its current notice before a visit.

The longer Llyn Celyn start was described as having a toilet block in a 2023 guide; current opening is unconfirmed. Bala is the nearby service town and has T3/T3C buses. Arrange the onward transfer to the Arenig starts and the return journey separately. Before travelling, check Natural Resources Wales access notices and local signs.

Rock and remembrance

The summit ridge exposes volcanic tuffs, including quartz veins, fractured rock and evidence of glacial erosion. Arenig Fawr also gave its name to the historic Arenig stratigraphic series.

The summit plaque remembers eight American aircrew killed on 4 August 1943, when B-17F 42-3124 crashed during a night training flight. The original 1945 slate plaque was replaced in bronze on 31 August 2019. Treat the memorial and any aircraft remains respectfully.

In clear weather the view takes in Yr Wyddfa, the Glyderau and Carneddau, the Rhinogydd, Cadair Idris and the Aran range.

Name

Fawr means great or big, contrasting with Fach, little. Visit Bala describes Arenig as a diminutive of Aran.