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.
(..) Do you speak any English? OK. Alright, thank you. "That Paris exists, and anyone could choose to live" "anywhere else in the world, will always be a mystery to me." "Dinner with...Dinner with Pablo, and Henri Matisse." "Pablo is the greater artist, but Matisse is the greater painter." (..)2011 Midnight in Paris