The Great Wall of China

The Great Wall of China was probably the biggest no-brainer on the list. I haven't seen vote totals but I'd be shocked if this wasn't the top vote getter. (The Pyramids would be in the same category if they weren't on the old list.)
The oldest parts of the wall date back to the 3rd century BC. It was made with wood and stone and rammed earth. The brickwork wall that forms our modern idea of the wall was started in the 1400's.
It's the longest man made structure, roughly 4000 miles long. That's longer than the drive from New York to LA.
Contrary to popular myth, it can't be seen from the moon. Even Astronauts in the shuttle can't see it. It's plenty long enough, but far to skinny, only 30 feet across at it's widest. It's also a similar color as the surrounding area.
My cousins visit was captured here: