Cwm Idwal

Cwm Idwal is a textbook cirque: a bowl scooped by a glacier out of the Glyderau, holding Llyn Idwal, with moraines across its floor and the Devil's Kitchen, a dark cleft in the headwall, above. Charles Darwin visited in 1831 studying rocks and returned in 1842 having read Agassiz on glaciation, and wrote that the evidence of ice was so obvious that a house burnt down by fire would not tell its story more plainly, yet he had missed it entirely the first time; the passage is a standard example of how theory shapes what is observed. It became the first national nature reserve in Wales in 1954, protecting arctic-alpine plants that survive on ledges out of reach of sheep, including the Snowdon lily. The Idwal Slabs are among the birthplaces of Welsh rock climbing.

What you actually see

• The glacial bowl - a cirque with moraines and a lake on its floor.
• The Devil's Kitchen - a dark cleft splitting the headwall above the lake.
• The arctic-alpine ledges - rare plants surviving where sheep cannot reach.
• The Idwal Slabs - climbing routes worked since the early twentieth century.

When to go

April to October; alpine plants flower in June and July. The cwm holds cloud and rain often, and the path is rough. Winter turns the Devil's Kitchen into a serious ice climb and the approach into a mountain route.

Honest expectations

The path from the car park is stony and steep in places, and the circuit of the lake is rougher than it looks. The Devil's Kitchen scramble is genuinely hazardous in wet conditions. Ogwen parking is charged and full early on fine days.

Nearby

Tryfan rises across the valley; the Ogwen valley runs down to Bethesda.