Llyn Idwal.
The gloomy horrors of the surrounding scenery exceed even those of Ogwen;
the encircling cliffs are overhanging, broken, and dark; in one part the
whole mountain is rent asunder, and the chasm of Twll dû (or the Black
Cleft) gapes between the terrific masses. The solitude of Cwm Idwal
proved favourable to the perpetration of a deed of blood, and it was here
that young Idwal, the infant heir of Prince Owen Gwynedd, was
treacherously assassinated, by order of his foster-father Nefydd, to
whose care his father had consigned him.