There's no 'mystery' (to/as to/about) why we're here. = It's no 'mystery' why we're here. [=we know why we are here]
His success is something of a 'mystery'. = His success is a bit of a 'mystery'.
We'll reveal the identity of today's 'mystery' guest after these commercials.
(..) Why did God have to give me that stupid penis? I don't know. Any more than I know why he gave men nipples. There are mysteries. And as a Catholic, I enjoy them. The mysteries, that is. Well, I enjoy the nipples. So now they think that I'm a liar. That I made it up. (..)2013 TvShow: Orange Is the New Black Title: The Chickening Season: 1 Episode 5