Snowdon (Welsh: Yr Wyddfa, pronounced [ər ˈwɪðva]) is the highest mountain in Wales, at an elevation of 1,085 metres (3,560 ft) above sea level, and the highest point in the British Isles outside the Scottish Highlands. It is located in Snowdonia National Park (Parc Cenedlaethol Eryri) in Gwynedd, and has been described as "probably the busiest mountain in Britain". It is designated as a national nature reserve for its rare flora and fauna.
The rocks that form Snowdon were produced by volcanoes in the Ordovician period, and the massif has been extensively sculpted by glaciation, forming the pyramidal peak of Snowdon and the arêtes of Crib Goch and Y Lliwedd. The cliff faces on Snowdon, including Clogwyn Du'r Arddu, are significant for rock climbing, and the mountain was used by Edmund Hillary in training for the 1953 ascent of Mount Everest.
The summit can be reached by a number of well-known paths, and by the Snowdon Mountain Railway, a rack and pinion railway opened in 1896 which carries passengers the 4.7 miles (7.6 km) from Llanberis to the summit station. The summit also houses a cafe called Hafod Eryri, open only when the railway is operating and built in 2006 to replace one built in the 1930s. The railway generally operates to the summit station from Whitsun to October. The daily running schedule depends on weather and customer demand.