A canyon in Kazakhstan some hundred and fifty kilometres long, one stretch of which is called the Valley of Castles — sedimentary rock cut by wind and water into towers and walls up to three hundred metres. On its floor stands a grove of Sogdian ash that survived the Ice Age, a species found almost nowhere else. Kazakh tradition fills the canyon with spirits, and locals advise against sleeping on the floor of it — not for mystical reasons, but because the water rises without warning.