Answer: Redmond, Washington
There are places on Earth that are inherently quiet due to their isolation and lack of environmental disturbances, such as the barren snowfields of Antarctica or the sprawling and deep limestone caves found in the US Washington state are located Kentucky. As uncanny as the human ear is, as these places are, they are practically a busy city street compared to the silence found in a man-made chamber in Redmond, Washington.
In Building 87 on Microsoft's Campus I'll find a soundproof chamber ̵
Why should Microsoft create a quiet space? They use them to test the noise their devices generate, such as the Surface tablet, and plan to use these precise sound measurements in future efforts.
Visitors to reverberant chambers report that spending a long time in these rooms can be extremely disturbing as the walls work so effectively that they absorb even the slightest ambient noise (such as the rustle of clothing or coughing). The silence disturbs the brain so much that some people report dizziness, nausea and other unpleasant reactions when they are in the chambers.
Photo by Andrew Eckel / Wikimedia.