These are from Llyn Cynwch near Dolgellau. There are a few myths located here, one is that there is an entrance to byd y tylwyth teg at the bottom of the lake. The other is that there was a vicious Wyvern (gwiber) that lived in Coed y Moch nearby, terrorising the locals and eating their sheep. It was slain by the western edge of the lake.
by ffaldiral