Llyn Arran (Llyn Aran) sits in a rather desolate and remote spot beneath Cader Idris and is the source of the Afon Aran which is one of the two rivers that dissect Dolgellau (the other being the Wnion). Access is difficult, so many people only view it from above when walking along the ridge from Pen y Gadair to Mynydd Moel. When viewed this way you can see its almost square shape.
If you want to dip your toe into the lake, you’ll need to get to the top of the minor road to Bwlch Coch and its old radio mast and follow the uneven path over the rough grass, cotton grass and streams for over an hour (and you’ll be pleased when it does eventually come into view and you realise you are going the right way). It’s one of the walks to best avoid after moderate to heavy rain.