It is a truth universally acknowledged, that the Great Wall of China is “the only man-made structure visible from space.” Why on Earth does that thought escape anyone’s lips? It takes less time to realize how stupid it is than it does to actually say the sentence aloud. The important, and impressive, fact about the Great Wall is how long it is, not how wide, and why would length alone ever be a factor in determining whether or not you can see something from a great distance? It is clearly less wide than any major highway (most of which also tend to be pretty long), and basically the same color.
This is the kind of thing I could only imagine becoming a myth before we could go into space and see how stuff looks like from orbit, (even though, for the extremely obvious reasons listed above, it would still be a stupid idea), and in fact, it does appear to date to at least the 1930s, in the form of “the GWoC is visible from the moon.” What?! Continents are barely visible from the moon.
This obviously completely wrong fact is even printed in Chinese textbooks. There have been many complaints about the lousiness of our textbooks, but at least our nationalistic garbage is vague and hard to convincingly disprove (to about 30% of people anyway). This obviously completely wrong fact is so ingrained in culture there that when their first astronaut was unable to spot it, panic ensued, and it took a second, American, astronaut taking the really indistinct picture above, to satisfy everybody. Seriously, that picture was plastered all over Chinese newpapers as evidence that this idiotic myth was true. Even though it was through a magnified camera lens and is still almost impossible to discern. I doubt it would have mattered, people everywhere else in the world already reflexively believe it to be true with no evidence or second thoughts in the first place anyway.