The Travels of an Alchemist: The Journey of the Taoist Ch'ang-Ch'un from China to the Hundukush at the Summons of Chingiz Khan (Paperback) (ISBN-13: 9780415758901)

First published in 1931.
Mainly focussing on cultural and geographical aspects, Travels of an Alchemist are unique in their importance as a source for early Mongol history, enabling us as they do to fix with certainty the otherwise obscure and much disputed dates of Chingiz Khan's movements during his Western campaign. The author, a Taoist doctor, left some of the most faithful and vivid pictures ever drawn of nature and society between the Aral and the Yellow Sea.
Waley's introduction provides excellent background information with which to place the Travels in their appropriate historical, social and religious setting.