Anyone who loves mountains knows K2. Rising steeply at 8,611m, above the Karakoram Range along the Pakistan-China border, it has come to be known as the ‘savage mountain'. Battered by atrocious weather, it forms a near-perfect pyramid, covered in hanging glaciers and gleaming under the shifting patterns of light and shadow. The silhouette of the long Southeast ridge of K2 (the Abruzzi ridge, by which K2 was first climbed in 1954) jutted through the clouds, it has always been the ultimate challenge for the world’s most experienced mountaineers and the graveyard for many of their ambitions. Its base camp is reached by a treacherous track along the Baltoro Glacier, a 63km river of ice. Of the 14 mountains that rise above 8,000 meters, K2 remains the only peak unclimbed during winter.