Cwm Idwal is a corrie located in the Snowdonia National Park. Cwm Idwal is a spectacular product of glaciation, surrounded by high crags, screes, moraines and rounded rocks, with a lake on its floor (Llyn Idwal). Cwm Idwal comprises volcanic and sedimentary rock which was laid down in a shallow Ordovician sea, and later folded to give rise to the distinctive trough-shaped arrangement of strata known today as the Idwal Syncline. This fold in the rock is visible today, thanks to the layering of the sedimentary rocks. The area was then eroded by glacial action to form the classic semicircular valley.
It is accessible via the A5 and there is plenty of parking. Toilets are available to the public.
It is a 20 minute walk up to Cwm Idwal from the car park. These two managed it ok:
You can view images of Cwm Idwal and the Nant Francon valley on Geography Photos by Internet Geography.