From Wikipedia, the free encyclopedia. Snowdonia (Welsh: Eryri) is a region in north Wales and a national park of 823 square miles (2,130 km 2) in area. It was the first to be designated of the three national parks in Wales, in 1951.he English name for the area derives from Snowdon, which is the highest mountain in Wales at 3,560 ft (1,085 m). In Welsh, the area is named Eryri. One assumption is that the name is derived from eryr (eagle), but others state that it means quite simply Highlands, as leading Welsh scholar Sir Ifor Williams proved.