Introduction to the copper wall and iron wall: The copper wall and iron wall is located at the entrance of Tianmen Cave. After years of baptism, it has formed a natural barrier. It is very much like a barrier that hides the fairyland, and it is also a screen that separates the fairyland from the human world. The copper wall and iron wall are a smooth stone wall formed in the entire karst landscape environment by hundreds of millions of years of natural power and thunderous geological movements. Due to faults and years of weathering, the stone wall belongs to the Paleozoic Era 250 million years ago. Permian Changxing Formation limestone.