The Snowdonia National Park covers 845 square miles comprising mountain, moorland and forest, interspersed with deep valleys, and extends to the coast at Cardigan Bay. Among the mountain ranges are the Carnedds, Cader Idris, the Glyders and the Snowdon range. Of Snowdon's five peaks, the loftiest is Y Wyddfa which rises to 3,560 feet - the highest mountain in Wales. By far the easiest way to ascend Snowdon is by the picturesque Snowdon Mountain Railway, the only rack railway in Britain. The track climbs from the lakeside terminus at Llanberis to a point about 70 feet below the summit. Llanberis Pass, a deep cleft in the mountains where the River Seiont dashes down beside the road, provides some of the most spectacular views in all Wales. At the foot of the pass are Llyn Pens and Llyn Padarn, separated by a neck of land and guarded by Dolbadarn Castle, once a stronghold of the 13th century princes of Gwynedd.