Andrew - secret.
I'm not going with the obvious - Secret deodorant or The Secret (the recycled ideas in a book/DVD of the same name).
We all have secrets.
And we all can be seen as mysterious because we have them.
Some are very private hence the nature of the word secret.
But, how do we keep them and can we always keep them clandestine?
A secret wall, or secret passage?
My Dad once owned a building which had a false wall, revealing a staircase to a "secret" room. This room contained lovely old antiques, stored away for well over 80 years. Because it was next to an old railway line, everything was covered in black soot. The building was once a general store, and the owner was clearly a Freemason, a secretive order, if you will. He was clearly the secretary, as there were books and books on minutes of the meetings. But what I remember more, was a beautiful Eaton's brass headboard, with the sticker still on it. I still have that brass headboard.
So, from this secret room, hidden by a secretive man, who belonged to a secretive "club" all was revealed. Not sure why it needed to be a secret, but, proving, that sometimes it is hard to keep a secret forever.