Snowdon. Snowdon is the highest mountain in Wales, at an elevation of 1,085 metres above sea level, and the highest point in the British Isles outside the Scottish Highlands. It is located in Snowdonia National Park in Gwynedd. It is the busiest mountain in the United Kingdom and the third most visited attraction in Wales, with 582,000 people visiting annually. 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 paths, and by the Snowdon Mountain Railway, a rack railway opened in 1896 which carries passengers the 4.7 miles from Llanberis to the summit station. The summit also houses a cafe called Hafod Eryri, open only when the railway is operating; it opened in 2009 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. The name Snowdon is from the Old English for snow hill, while the Welsh name-Yr Wyddfa-means the tumulus orthe barrow, which may refer to the cairn thrown over the legendary giant Rhitta Gawr after his defeat by King Arthur. As well as other figures from Arthurian legend, the mountain is linked to a legendary afanc and the Tylwyth Teg. A 1682 survey estimated that the summit of Snowdon was at a height of 3,720 feet; in 1773, Thomas Pennant quoted a later estimate of 3,568 ft above sea level at Caernarfon. Recent surveys give the height of the summit as 1,085 m, making Snowdon the highest mountain in Wales, and the highest point in the British Isles outside Scotland. Snowdon is one of three mountains climbed as part of the National Three Peaks Challenge. The environment of Snowdon, particularly its rare plants, has led to its designation as a national nature reserve. In addition to plants that are widespread in Snowdonia, Snowdon is home to some plants rarely found elsewhere in Britain. These include the Snowdon lily, Gagea serotina, which is also found in the Alps and in North America; it was first discovered in Wales by Edward Lhuyd, and the genus Lloydia was later named in his honour by Richard Anthony Salisbury. Snowdon lies in the northern part of Snowdonia National Park, which has also provided some legal protection since the park's establishment in 1951. The rocks which today make up Snowdon and its neighbouring mountains were formed in the Ordovician Period. At that time, most of modern-day Wales was near the edge of Avalonia, submerged beneath the ancient Iapetus Ocean. In the Soudleyan stage of the Caradoc age, a volcanic caldera formed, and produced ash flows of rhyolitic tuff, which formed deposits up to 500 metres thick. The current summit is near the northern edge of the ancient caldera; the caldera's full extent is unclear, but it extended as far as the summit of Moel Hebog in the south-west. Snowdon and its surrounding peaks have been described as true examples of Alpine topography. The summits of Snowdon and Garnedd Ugain are surrounded by cwms, rounded valleys scooped out by glaciation. Erosion by glaciers in adjacent cwms caused the characteristic arêtes of Crib Goch, Crib y Ddysgl and Y Lliwedd, and the pyramidal peak of Snowdon itself. Other glacial landforms that can be seen around Snowdon include roches moutonnées, glacial erratics and moraines. The English name Snowdon comes from the Old English snaw dun, meaning snow hill, as Snowdon often has a covering of snow. Although the amount of snow on Snowdon in winter varies significantly, 55% less snow fell in 2004 than in 1994. The slopes of Snowdon have one of the wettest climates in Great Britain, receiving an annual average of more than 200 inches of precipitation. A number of lakes are found in the various cwms of the Snowdon range. Llyn Llydaw-1,430 feet high, 110 acres-lies in Cwm Dyli, Snowdon's eastern cwm, and is one of Snowdonia's deepest lakes, at up to 190 ft deep. Various explanations of its name have been put forward, including lludw, from ashen deposits along the shore, to Llydaw.