Llyn Idwal into Llyn Idwal from around Cwm Idwal. One small river flows out and joins the Afon Ogwen river at Pont Pen-y-Benglog near Ogwen Cottage, immediately above the Rhaeadr Ogwen waterfall. The lake is easily accessible on foot via a 900-metre long stone-paved path from Ogwen Cottage on the main A5 road. Another path encircles the lake. Two paths lead from opposite sides of the lake to the top of the ridge close to the Twll Du (Devil's Kitchen), but these paths become rather steep in places. They lead to Glyder Fach and Glyder Fawr. There is a small pebble beach
Glyderau and retreat of glaciers during the Ice Ages has worn down the mountains to their present proportions. The underlying rock is a mixture of sedimentary and volcanic material. The last ice sheet retreated about 10,000 years ago and Cwm Idwal is a good example of a cirque formed by the ice. The main glacier flowed down the adjoining Nant Ffrancon Valley, a route now followed by the A5 road, and Cwm Idwal housed a side glacier. The ice scarred the surrounding cliffs, hollowed out the bed of Llyn Idwal and dumped rocks and other material that formed moraines at its