What are the three landmarks that man has made that you can see from space?

There are two for sure that can be seen most of the time unaided. They are The Great Wall of China and the Ancient pyramids at Giza, Egypt. There are other structures that can be seen from space, but the conditions must be perfect and sometimes the view must be aided by cameras. The Great Wall of China can be difficult at times due to the fact it is constructed of the same materials that surround it, so it tends top 'blend in".