MONGOLIA // About twice as high and four times as long as the Sahara's famous Erg Chebbi dunes, the Khongoryn Els range in Mongolia's Gobi Desert features some of the largest and most spectacular sand dunes in the world. At up to 300m (985ft), the climb is an exhausting slog that can take the best of an hour, but the views of the desert from the sandy summit are wonderful. Before you lies an undulating blanket of pillow-soft mounds, which intensify in colour from mellow yellow to burnished gold as the day goes on. Locally they are known as Duut Mankhan - the Singing Dunes, a nod to the lilting sound they make when the sand is moved by the wind or as it collapses in small avalanches. Magically, as if from nowhere, locals will appear leading camels to whisk you away.