I've been contemplating my navel recently. Mine is about 22mm deep. I used my new 10 megapixel digital camera with a super-macro LED assisted function to go exploring down there. I was pleasantly surprised. It is an almost perfectly round little funnel. It bottoms out with the fold on the bottom and to the right--and not a speck of dirt or dust in there. I had to pull a thorn out of there once when I was a kid and I have kept it pristine ever since. Note to other self explorers: Shave. Hair obscures the very complex topography of the human belly...