Did you know your TCP/IP stack leaks information on your physical location?
This website demonstrates IP address geo-location by passively measuring TCP/IP round-trip times of web requests made to a few servers spread around the world. The measurements are then used to approximate possible physical distances to the servers, and finally drawn on a Google Map. The common area of all circles (that is, the most shaded area) shows your likely location.
Sorry, the demo was shut down on 5th July, 2016. Thanks for watching :)
See also: whereami.pl