Khongoryn Els sings, but only when the sand is bone dry. Break the crest of a slope with your foot and the little avalanche you set off makes the whole dune let out a low boom. It is one deep note somewhere between 70 and 105 hertz, closer to a propeller plane than to anything you expect sand to do. Mongolians call the place Duut Mankhan, the singing dunes. Rain, or even a heavy dew, is enough to shut it up, and the sound comes back only once the sun has baked the moisture out. The sand is piled into a wall about 100 kilometres long and up to 12 kilometres wide, its highest crests standing hundreds of metres over the gravel plain.
Three landscapes meet in one frame along the northern edge. A thin stream, the Khongoryn Gol, holds a ribbon of meadow green against the gold, fed by water moving underground from the Sevrei and Zoolon ranges. The camels and horses of herding families graze on it while bare dark mountains close the view behind. Climbing the tallest crest is slow, thankless work: the slope gives way under every step, and there is no shade and no water on it. The ridge at the top is narrow enough to sit astride, with dune waves running to the horizon on one side and the herds reduced to specks on the other. Then you sit down, slide, and the dune answers you. Nomadic families still live at the sand's edge with their two-humped Bactrian camels and rent felt ger tents to travellers. The whole field covers some 965 square kilometres and has been protected since 1993 inside Gobi Gurvansaikhan, Mongolia's largest national park.