Fractal Cross ‘n’ Boxes

Interesting how a very square up-down left-right set of rules produces such diagonal negative space…

DIRECTIONS: 

1. Start with a box.
2. Draw boxes on the middle of each available interior side.
   (1st iteration = 4 interior sides, 2nd iteration = 20 sides, 3rd iteration = 100 sides…)
   –> (# sides at step n = 4×5[nth power])
3. When that gets too small to see, start dividing each small box into quarters… and so on.