In the early 1980s, ambigram master and puzzle designer Scott Kim created the following image while performing some font experiments. He made a font in which black and white spaces were equally wide, and then had fun exploring what he could do with it.
More examples of Scott Kim’s ambigrams (which he calls inversions) can be found here. He also created a very nice Joy to the World animation for a family holiday card that is worth a look (or another look if you are already familiar with it!).
(via Scott Kim)