Cave is perhaps the wrong term. These are not natural rock structures but dugouts formed by hand from the loess earth. Hills in the area are like Swiss cheese, filled with holes. Even the former Chinese leader Mao Zedong lived in a cave: Communist commanders used the caves of Yan’an, to the north of Xi’an, as headquarters from the 1930s to ’40s, and during Kuomintang airstrikes the dugouts provided protection as the rest of Yan’an was destroyed.

Julia Bartaux, manager of tour company Xi’an Insiders, first met Zhou when he was out walking his goat – a surprisingly common sight in Shaanxi. The company’s tour groups now frequently turn up to his cave in the village of Zhoujiagou. Zhou’s children are either unwilling or unable to take him and his wife into their own homes, so the elderly couple remains in the cave.

Today, most remaining cave dwellings are hooked up to mains electricity and some even have running water. But there is a big difference in the standard of caves; as with conventional homes, the size and condition of each cave reflects the economic means of the owners. Zhou’s consists of three connected rooms burrowed into a hill. But it stands in contrast to the residence belonging to the Wang family in Xi’an’s Hanyu village, which is little different to a house. Visitors to the area can stay here through Xi’an Insiders’ tours, and it’s even offered on the online homestay service Airbnb.

The Wangs’ residence is grander than most cave dwellings. Here, the centre of a hill was removed to create a central courtyard with caves opening onto it. Liu Yanlian, Wang’s wife, looks after the home’s four bedrooms and kitchen. ‘Maintaining a cave takes time and energy – most caves are just in the side of a hill and are under great pressure,’ she says, before continuing with a laugh, ‘but that’s the man’s job.’