It is hard to describe it without seeing it for yourself, but the link below is to a flash application which shows the various scales of the universe. From the inconceivably large to the smallest physically possible, the interactive scale below shows that our human conceptions of “large” and “small” are almost comically lacking in completeness.

You can find the scale here. [Make sure to turn your volume up for proper effect]

The scale covers a wide range of scientific concepts, so make sure to click on the aspects of the scale that you want to learn more about (I’d recommend checking out the “Planck length,” it’s mind bendingly small, in fact it’s the smallest).