What's the largest man-made structure in the world?

The Great Wall of China is the largest man-made structure in the world; it is visible from space*, and has been photographed from space.

* Editor note: NASA doesn't entirely agree with "visible from space". See below.

In 1991, the Great Wall of China became the second largest man-made structure in the world. The largest was Fresh Kills Landfill, serving New York City.

link for above

" Opened in 1948, it became one of the largest refuse heaps in human history. The site is 12 square km (4.6 square miles) in area; and when operational twenty barges, each carrying 650 tons of rubbish, were shipped in every day.[2] Had Fresh Kills stayed open as long as originally planned it would have grown to be the highest point on the East Coast of the United States. It could be regarded as being the largest man-made structure on Earth, with the site's volume eventually exceeding the Great Wall of China. In fact in 2001 its peak was 25 meters taller than the Statue of Liberty. "

https://en.wikipedia.org/wiki/Fresh_Kills_Landfill

As for GWoC being visible from space.....

" For some reason, some urban legends tend to get stated and never disappear. This legend even appears as a erroneous Trivial Pursuit question. The legend? Many are familiar with the claim that the Great Wall of China is the only man-made object visible from space or from the moon with the naked eye. This is simply not true. "

http://geography.about.com/od/specificplacesofinterest/a/greatwall.htm

" It has become a space-based myth. The Great Wall of China, frequently billed as the only man-made object visible from space, generally isn't, at least to the unaided eye in low Earth orbit. It certainly isn't visible from the Moon. "

http://www.nasa.gov/vision/space/workinginspace/great_wall.html

This is a tricky question to answer. First you must define "largest". But if I was forced to answer I would say The Great Wall of China and The U.S. Highway System.

I'm thinking largest by volume. One of them is the Great Wall of China. What's the other?

More famously, the largest man-made object in terms of weight and 3-D volume is the Three Gorges Dam spanning the Yangtze River in China. As previously mentioned, the dam weighs about 34 million metric tons, has a length of 2,335 m (7,661 ft) a height of 185 m (607 ft), width (at the base) of 115 m (377.3 ft). A close runner-up is the Terminal 3 building at the Beijing Capital International Airport, which covers 240 acres and is nearly two miles long.
http://www.wisegeek.com/what-is-the-largest-man-made-object.htm
Also see posts about the Fresh Kills landfill.

Update on the landfill mentioned above:

"In October 2008, reclamation of the site began on a multi-phase, 30-year site development for reuse as Freshkills Park."

So it appears the landfill is no longer larger than the great wall.

So my vote is that the great will of China is once again the answer to this question.