Have you ever seen those posters where the picture of something -- say, a Shuttle Orbiter -- is made up of littler pictures? The main picture is divided into a gazillion little squares, and each one of those squares is another picture. It's pretty cool; from a distance the picture looks fine, then up close you can see all the little pictures making it up*.
Not sure what I mean? Then check out this awesome interactive National Park picture put up by National Geographic.
When you go to that site you see this:
The yellow square defines a "region of interest" which you can move around. When clicked, you get a zoom:
See? Again, the yellow square, and again when you click, another zoom:
Coooool. Technically, you can keep on doing that forever, but in this case it drops a few levels and then you get a description of one of the component pictures.
This is a pretty nifty way to get people to click around, look at amazing nature photographs, and then actually learn something, too. It really is a lot of fun to click away at the infinite picture, so go ahead and give it a try.
Tip o' the infinite derby to Michael Allen.
* I'm guessing, but I think the way it's done is the big picture is digitally divided into little squares. Each square then has its average color calculated, and matched to a smaller picture with that same average value. Replace each square of the big pic with the corresponding little pic, and voila!