Completely Artificial Problem
There was a time I was in Bucharest for a tournament. One Saturday evening I went with some Go players to a friend of ours to drink some beers and analyze our games. Late in the night Cristian Pop 6 dan showed us this problem, saying he knows it from Leszek Soldan 6 dan from Poland :-).
We looked at it for about a quarter of an hour and nobody got the right answer. Some were on the right way but couldn't go to the last move. Then Cristi showed us the answer and we could continue our beers.