The Question:

Is the Great Wall of China really the only manmade structure that can be seen from space?

The Answer:

Nope.

The original formulation of this claim—which predates space travel—was that the Great Wall of China was the only manmade structure that could be seen from the moon.

It cannot, in fact, be seen from the moon, at least not with the naked eye. At some lower altitudes it might be visible from outer space, especially with the use of binoculars, but it's hardly the most visible manmade object. While the wall is long, it is only a few meters wide, and it's not very different in color from its surroundings.

For more on this specific issue, see What's Really Visible from Space at Space.com. Otherwise, you might be interested in more Famous Buildings and Structures.

—The Fact Monster