Book excerpt: The third in Sven Hedin's Central Asia trilogy, The Wandering Lake is arguably his most famous work and a rare account of a now-vanished world. The lake of Lop Nur, the 'heart of the heart of Asia', is one of the world's strangest phenomena. Situated in the wild Chinese province of Xinjiang, Lop Nur - 'the wandering lake'- has for millennia been in a perpetual state of flux, drifting north to south, often tens of kilometres in as many years. It was once the lifeblood of the great Silk Road kingdom of Loulan, which flourished in this otherwise barren region 2,000 years ago, and its peculiar movements confused even Ptolemy, who marked the lake twice on his map of Asia. Following 'the pulse-beats of Lop Nur as a doctor examines a patient's heart', Sven Hedin became captivated by its peripatetic movements and for forty years his destiny was inextricably linked with that of this mysterious lake and the region surrounding it. His last journey to Lop Nur was in 1934, just days after he was released as a prisoner of General Ma Chung-yin (the rebel leader of Xinjiang). Travelling the length of the Konche-daria and Kum-daria rivers by canoe, Hedin embarked on his last Central Asian expedition and proved what he had always suspected - that Lop Nur did indeed shift position - and why. When he camped on its vast banks at night, Lop Nur was deep and full. Today, this once great lake - a mighty reservoir in the desert - is nothing but windblown sand and salty marsh. A gripping story of adventure and discovery, The Wandering Lake is a masterpiece by one of history's last great explorers.