[Belly Button]

Now this is incredibly easy to answer and I see both answers that immediately come to my own mind have already been suggested!

Firstly, above all else, the ability to become pregnant and go through all those experiences. 

Secondly, yes, I'm going to have to admit this one myself - women's orgasms. As human body 'pleasures' or 'experiences' go, that surely must have to be right up there...