Corn Du the last ice age by ice scouring out hollows below the peaks, the water being partly dammed by moraines of rock debris carried down by ice action subsequent to plucking and frost shattering. Corn Du Corn Du is a mountain immediately to the southwest of Pen y Fan and the second highest peak in South Wales at 873 m (2,864 ft), situated in the Brecon Beacons National Park. The summit itself is marked by a well structured Bronze Age cairn with a central burial cist like that on nearby Pen y Fan. The two summits are visible from great distances
Pen-y-Gwryd Plas y Brenin. The Old Miners' Track from the Snowdon copper mines are now part of the modern A4086 road between Pen-y-Gwryd and Pen-y-Pass. It continues northwards beyond Pen-y-Gwryd skirting Glyder Fach to Bwlch Tryfan and Dyffryn Ogwen. From Pen-y-Pass is the "PYG track", one of the many routes leading to the summit of Snowdon, its name is believed be derived from the initials ("P-y-G"). However, older maps show it as the "Pig track", a name derived from "Bwlch y Moch" (the Pigs' Gap). During Roman Britain, the Roman Army built a marching camp at the head of Dyffryn Mymbyr