The Kernel is the part of an operating system that interfaces with the hardware, handling all of the most commonly used and tedious tasks such as writing to disks and actually sending signals on a network.

This is a video showing a 3-d print out of all of the pages of code in the linux kernel, as of 2006 of course.

It may not be news, but I still want to put up a link to it because it is a great example of what documentation can do.