You might be able to see the Great Wall of China from a low orbit in space, but in as little as 20 years, you might not be able to see it at all. Standing tall for over 2,000 years, it was originally built to protect China from enemy invasions. Today, the Great Wall of China is not only one of the world's largest man-made structures, but also one of the world's most visited tourist destinations. Unfortunately, two-thirds of the wall have been destroyed by over-farming. While restoration and preservation efforts are in effect, the wall is still facing erosion and damage from locals selling its bricks. If you want to see the Great Wall of China before it's gone for good, skip the rocket ship and hop on a plane instead.