That's one great idea NightWish
I scrolled trough the old thread and found that this is very amusing
My first question is: Is the member which riddle gets accepted allowed to participate in other 19 riddles guessing or not?
Second can you explain me the prize, meaning what is the voucher for?
One of mine suggestion is that if the riddle is about post/thread that those thread/post's are at least from 2009 - 2011. Because it will be very hard to find a post/thread from a couple of years ago