There's been a lot of buzz about this in library circles over the last half year, but I don't think I ever got around to posting links on here. Edinburgh has (had? no, has) a library phantom - an artist who left a series of paper sculptures in libraries and museums. She has remained anonymous, but recently left a last sculpture along with a note explaining only a little of the mystery (i.e. that she was a woman and not a professional artist) and saying that this was the last of ten scupltures (at the time that note was found, only eight sculptures were known - thankfully, once everyone knew to look for two more they turned up pretty quickly).
A brief article on the subject. Seriously, flip through those photos. These sculptures are amazing. One hopes they'll be preserved and exhibited for future visitors - I understand that three of the ten are currently up for display in the places where they were found.