The Greatest Cwm - Idwal

This walk offers some of the most dramatic mountainous scenery in the UK at the oldest National Nature Reserve in Wales

an ice age sculpted Glacial Cwm - a bowl-shaped hollow filled with the crystal clear waters of Llyn Idwal. The site is world famous for its rock formations and its rare and fragile plant life.

now in the ownership of the National Trust - this is a must do walk for anyone who visits Snowdonia
The rocks of Cwm Idwal were formed over 400 million years ago, when North Wales was a land still underwater and being formed by volcanic explosions.

Charles Darwin visited Cwm Idwal in 1831, and observed that the large, scattered boulders at Llyn Idwal contained marine seashells. He realised that the rocks must have formed within an ancient ocean, and therefore had been later uplifted to the surface by forces within the Earth’s crust.
Darwin later returned to the area, and made a further observation- that the beautiful landscape of Cwm Idwal was shaped by glaciers, at a time when Wales was far colder than it is today.
Glaciers move incredibly slowly, and carve steep-sided valleys as they erode the rock beneath them. The larger the glacier, the deeper the valley it can erode; where small glaciers feed into a larger glacier system, small ‘hanging valleys’ are created high above the floor of the main valley. The word “Cwm” is Welsh for valley, and Cwm Idwal is a striking example of a glacial hanging valley.