About 90 km west of Dunhuang in the open Gobi, a square mud-brick fortress called the "Small Square Fort" is what survives of the Han-dynasty Yumen Pass — the Jade Gate — through which Khotanese jade and Persian glass entered China and Chinese silk left it. The walls are eroded but still ten metres high, the gateway still recognisable, and the silence of the surrounding desert is total. No tour-bus crowds, just gravel, wind, and a few wandering camels.
Visiting requires a half-day excursion: the standard arrangement is to share a private car (around 300 RMB per car) that combines Yumen Pass with the nearby Han-dynasty Great Wall ruins and the Yardang Geopark — a long but extraordinary drive across the Gobi. Bring water, sunscreen and a hat; there is almost no shade.