Man has always made caves, underground shelters, storage rooms, escape tunnels and so on. Mining has also created a lot of artificial caves. Some really old caves are rather mysterious. The underground cities in Turkey, for example, are truly enigmatic because of their sheer size (twelve stories underground) and their engineering (ventilation and water supply). There are many underground cities all over the world, and they are very ancient, as their builders are unknown. Some questions are still unanswered, such as why did they live underground, and what kind of lighting did they have (no sooth on the ceiling)?
In the 1990s some remarkable artificial caves were found in Longyou, China. Although some caves had structural damage, like collapsed roofs, some of them were remarkably well-preserved. As soon as they had been discovered the questions arose: who built them, why and how? They had been constructed with an unusual architectural plan that required some engineering to cut them out of the local rock, and this was most likely done with machinery. The problem is that they were found in a region that had never had any human occupation in written history. So they are very old. Luckily, the Chinese government opened five of these caves for tourism. In spite of that the Longyou Caves are not that well-known, at least not in the Western world. Most websites in the English language contain conflicting information, and information and pictures are often copied from each other. So, I dug a little deeper and looked into Chinese websites and a scientific research report that gives a much clearer look at these magnificent caves. The result you can see in my article of the Longyou Caves or Caverns.