The expedition continues its journey westwards through Turfan, The Land of Fire, visiting a dried-up lake 150 metres below sea level, and the Fire Mountains on the way.
There is very little archeology or art in this episode. The expedition flies over the desert in search of the ruins at Dan-dan Oilik, which was visited by Aurel Stein, but fails to find it as it had been covered by the desert at the time.
This episode sees the expedition crossing the southern route of the Taklamakan desert, which in the Uighar language means the place from which no living thing returns.
The Kingdom of Lou-lan was an ancient Buddhistic kingdom which used to house 4,000 monks, a quarter of the population, but the remains are sparse indeed, as it disappeared into the desert it arose in, long ago.
The Dark Castle of the title refers to the fortress at Khara-khoto, which was a main center of the Tangut state. The Castle has legendary status amongst the local people, who fear to go there, but the crew find some guides and trek across the desert on camels.
This episode focuses on the magnificent Mo-gao caves at Dun-huang in the Gobi desert. In this complex, there are 500 caves and over 3,000 statues and murals. It is counted as the longest art gallery in the world.
This episode sees the expedition crossing first the Yellow River, with its goat-skin rafts and giant waterwheels, and entering the Gobi desert along the He-xi corridor, where it visits some of the main citadels along the route.