At a glance
Llyn Idwal (LL57 3LZ) is a glacial lake in Cwm Idwal NNR — Wales's first National Nature Reserve (1954). 20–30 min walk from Ogwen Cottage car park on the A5. Wild swimming possible (very cold). Devil's Kitchen cliffs above. Starting point for Glyderau mountain routes. Snowdon Sherpa bus S6 to Ogwen. Free lake access; car park charge.
About Llyn Idwal
Cwm Idwal is one of the most dramatic glacial cwms in Wales — a deep cirque carved by glacier ice from the rock of the Glyderau, enclosing a lake on three sides with cliffs that rise to over 900 metres above. The lake occupies the floor of the cwm, reflecting the encircling mountains and the vertical cleft of Twll Du (the Devil's Kitchen) in its surface when the air is still.
The cwm was designated Wales's first National Nature Reserve in 1954, primarily for its geology and its extraordinary arctic-alpine botany. The combination of north-facing aspect, high altitude, thin soils and frost-shattered rock creates conditions for plants more typical of Scandinavia than Wales — Snowdon lily, purple saxifrage, mountain sorrel and several rare sedges grow on the cliffs above the lake. Charles Darwin visited Cwm Idwal in 1842 and recognised the evidence of glaciation in the striated rocks and transported boulders — a key early observation in the development of glacial theory.
The walk from Ogwen Cottage on the A5 is short and well-maintained — most visitors reach the lake without difficulty. Beyond the lakeshore, the terrain becomes mountain country: the ascent to the Glyderau plateau is steep, rocky and demands experience and navigation ability. For visitors who want the dramatic scenery without the mountain commitment, the lake itself and its immediate surroundings are outstanding.
Safety information
Wild swimming carries serious risks. Never swim alone. Tell someone where you're going and when you'll be back. Enter the water gradually to avoid cold-water shock. Know your exit point before you start. Wear a tow float and consider a wetsuit even in summer — Welsh lake and sea temperatures rarely exceed 16°C.
In an emergency call 999 and ask for the Coastguard (sea) or Police / Mountain Rescue (lakes & rivers). Nearest A&E: Ysbyty Gwynedd, Penrhosgarnedd, Bangor LL57 2PW. Tel: 01248 384 384.
Find it on the map
Frequently asked questions
The walk to Llyn Idwal starts from the Ogwen Cottage car park and visitor facilities on the A5 at the western end of Llyn Ogwen (postcode LL57 3LZ). A clear, well-maintained path leads up into Cwm Idwal and reaches the lakeshore in approximately 20–30 minutes (0.7 miles). The path gains approximately 100m of height and is suitable for most walkers including older children. The Snowdon Sherpa bus (S6) stops at Ogwen Cottage.
The Devil's Kitchen (Twll Du in Welsh — "Black Hole") is a dramatic vertical cleft in the cliffs at the head of Cwm Idwal, high above the far shore of Llyn Idwal. Water seeps through the cleft and the dark shadow within the cliff gives the impression of a sinister fissure in the mountain. The Devil's Kitchen is a famous landmark visible from the lake and forms part of the harder mountain routes up to the Glyderau plateau. The cliffs below it are a noted botanical site for rare arctic-alpine plants.
Wild swimming does occur at Llyn Idwal, though the lake is extremely cold — fed by drainage from high mountain ground and shaded for much of the year by the surrounding cliffs. The water quality is generally good. As with all mountain wild swimming, enter slowly, assess conditions carefully, never swim alone, and be aware of the remoteness of the cwm. In summer the lake sees more swimmers; in other seasons the cold is severe. The NNR status means staying on the path and causing minimal disturbance.
Cwm Idwal was designated as Wales's first National Nature Reserve in 1954. The cwm is notable for its geology — the rocks are some of the most studied in Britain for their evidence of glaciation — and for its botany. The cliffs around the cwm support rare arctic-alpine plants including Snowdon lily (Gagea serotina), purple saxifrage, mountain sorrel and several rare sedges. Charles Darwin visited Cwm Idwal and was puzzled by the glacial features he observed — he later recognised them as evidence of glacial action.
Yes — Cwm Idwal is one of the starting points for the Glyderau plateau. From the lake, paths ascend steeply to Y Garn (947m) via the Devil's Kitchen or to Glyder Fawr (1,001m) via the Gribin ridge — both serious mountain walks requiring experience, navigation skills and appropriate equipment. The Glyderau page on this site gives full details of these routes.