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 park is governed by the Snowdonia National Park Authority, which is made up of local government and Welsh representatives, and its main offices are at Penrhyndeudraeth.