I visited Sossusvlei in Namibia in 2010. The most memorable experience of this sightseeing trip was walking onto the Deadvlei - being a marsh that has looong since dried out. The ambient temperature must have been approximately 40 degrees Celsius at 12 noon.
Not ever have I heard "silence" as I did that day. There was nothing...no wind.... no sound of birds... or insects....nothing. For 10 minutes I merely stood in awe - and finally, there was a slight buzzing as an insect passed by, accompanied by the sound of a very gentle breeze. I experienced being part of a different world - incredible.