Originally posted by Darrie
That position cant be legal in my humble opinion. The only way for the King to get to a2 is via the back rank, but then the rook cant get to b1, since the last move must have been Kc1. Where is my thinking error?
I think the answer is correct!
My first solution was this:
The problem here is, that I cannot tell what the position before was. I only know the king moved from d8 to c8 but I don't know which piece it took there (or if he took a piece at all). This is covered in BigDoggs answer: There must have been a knight on c1, because that is the only piece that can get there in the move before White's last move. It could not have been unoccupied because then it really seems to be an illegal position as you pointed out.