Most travellers picture the Great Wall as the crenellated stone parapets at Badaling near Beijing, but those date from the Ming dynasty. The original wall — built by the first Han emperors in the second century BCE to protect the new Silk Road from the Xiongnu — was made of rammed earth, layered with reed bundles cut from the local marshes, and a long surviving section runs through the desert between Yumen Pass and the Yardang park.
You can see a particularly well-preserved beacon tower with a stretch of wall attached on the road between the two, and the colour, scale and emptiness of the setting are powerful. The wall here is over 2,000 years old, older than anything Roman that still stands; you have to remind yourself of that as you look at what could be mistaken for a low, eroded sand dune. Combined with the rest of the desert sights in a day trip.