alekz suggested I try to do a fractal in Minecraft. So I did a 81x81x81 Menger Sponge. This was rather interesting to work out how to do and I'll try my best to explain it.

First thing I had to work out was how to do one row of the cube. You convert the position on a number line from base ten(0,1,2,3,4,5,6,8,9) to base three (0,1,2). If the number in base three has a 1 as any of its digits then the space is empty. Now to do it on a 2d plane its only when there is a 1 in the base three number and it happens in the same digit of the number. Any position where the X and Y in base three both match up to one of these patterns 1???, ?1???, ??1? or ???1 will be empty.

Example 2100 and 0122 would be empty while 1022 and 0111 would be filled.

To do this for a cube the planes on all three axes have to follow that same pattern.

This took over 45 minutes to run on my computer with the computer putting a block in place every 0.005 seconds.

Wiki: http://en.wikipedia.org/wiki/Menger_sponge