Olaf the Stout
I find riddles extremely fun. A couple sessions ago I sprung this one I found, on the pc's.
If you have it... You want to share it... If you share it... You no longer have it.
200 xp's if the pc's could figure it out with their non character brains. Divided by 4 pc's. They couldn't, so I allowed them each to make an Int check. Two of them passed a DC of 15 and so I gave them the answer, but cut the xp award in half to 100 for 25 xp each.
What's the answer? You can tell me. It will be our little secret!