The worn-down steps of the Great Wall of China.
If you ever have a chance to visit the Great Wall of China, you will quickly realize that the steps are uneven and very steep, making them difficult to walk up and down.
While time has certainly taken its toll, the stairs were deliberately designed with varying heights so that unsuspecting invaders who were unfamiliar with the wall would trip or fall, ultimately slowing them down.
Some other interesting facts that I learned about the Great Wall of China are that it is not one single wall. It is actually a series of walls with some parts in North Korea and Mongolia.
If all the walls were connected and straightened out to actually make one giant wall, it would be equivalent to 1.8 times the diameter of the Earth. The diameter of the Earth is 7,456 miles (12,000 km), whereas the Great Wall of China is 13,170 miles (21,196 km) long.
And contrary to popular belief, the Great Wall of China cannot be seen from space!