For the last week or so of our 5,000-kilometre Walking Home From Mongolia adventure, my expedition partner Leon McCarron and I have been following the Great Wall of China westwards along the ridges and valleys of northern Shanxi. Unlike the postcard perfect stone sections of the Wall near Beijing, here it consists of a one to three metre ridge of crumbly yellow earth, covered in grass and dotted with regular watchtowers (five-metre columns of yellow earth).
But while the wall may not be as well endowed here, it has still been a magical experience to walk along it. The watchtower silhouettes mark out a path to the far horizon.
It has also been an incredibly exhausting leg of the journey, as the wall does not simply follow one ridgeline, but dances from ridge to ridge, plunging into the valleys and gullies in between.
With all the scrambling up and down, and zigzagging along paths, we estimate we were walking about three kilometres for every two kilometres' progress.
This rugged country is sparsely populated and we have had to keep our eyes peeled for cave villages where the local shepherds and farmers live. These villages consist of homes and stables literally dug out of the hillside, with the roofs covered in grass and mud. People in these parts have lived in such dwellings for thousands of years, and in fact there are still over 30 million cave-living people in China.
The villages are usually built on the sun-facing southern slopes of hills, and as we are walking from the north, it's possible not even to see them until literally walking over the top of them. We often stop to fill up our vacuum flasks with hot water, and the inhabitants, although slightly taken aback by our sudden arrival, are generous and friendly. Mainly older people and their grandchildren remain - due to the mass migration of young people to the cities.