What was the last move?

I was looking on the net and found this puzzle which requires you to work backwards. I don't know who came up with the puzzle or if a solution even exists (although I have a feeling it was published by Mensa). If you think you have found a solution plz logically explain your answer in the comments below. Thank you. My brain hurts trying to work this out.

EDIT: Of course, this situation is almost impossible in normal play. Think hypothetical.

The question to the puzzle is: "What was the last move made?"

Well, let's see where logic takes us... the pawns could not have moved on the last move, this is obvious.  Also, the rook could not have moved, as it is currently surrounded on all sides by other pieces.  That leaves only the two kings, and the white knight.  The knight could only have moved to a1 from previously being on b3.  The white king could also have moved to c1 from d1.  As for the black king, in order for it to have moved to a2, it would have had to occupy either a3 or b3 on the previous move, putting it in check by one of the pawns (ignoring the knight for the moment).  Since the pawns cannot have moved AT ALL at this point in the game, the king would have had to have moved INTO check at a3 or b3 to do this, which is patently illegal.  So, that means black could NOT have moved last.

That leaves only the two possibilities: Kc1 or Na1.  I'm not sure how to decide between those at the moment, but I'll come back and think about this...

White starts it pieces on the first two ranks, and since pawns don't move backwards, we know it can't be a pawn move. Next, the black king couldn't have moved to a2 going down, but going around the pawns due to b2 taking control of a3 and c2 with b3. The black king couldn't move to a1 due to the Rook on b1, it can't take it because of the white king next to it, and can't capture the pawn because of the king and rook. It would've been white's turn from the last move with the Na1 where it was previously on b3 (there are no other places for the knight to be on due to a pawn in the way) because if it were black's move then it would be a stalemate.

Answer: Last move made by white with Knight from b3 to a1.

I thought it was Na1 also but looking further ahead, what was black's move before Na1? Sometimes I think that maybe black's last move was taken by the king on c1 so the only piece that could logically and legally get there would be a black knight. But I'm not sure how far beyond that I can go.

I would say a piece that was black's be on a1.

It seems pretty obvious that there had to be another black piece on the board prior to the last move - so one of white's previous moves (and maybe the last move also) was a capture of black's last piece.  However... if white's last move was Nxa1, then he just walked into a stalemate, when Rxa1 (with the knight still at b3) would have been checkmate - possible, but not the most likely scenario.  Then again, black walking his king all the way along the first rank BEHIND white's pawns without getting mated doesn't seem very likely either!!

This puzzle was a lot more confusing before I realized that white's last move was probably a capture of a black piece.

The last move Kc1 capturing a knight.

Since white's pawns are in their original positions, the only way black's king could possibly have arrived on a2 on his last move is via a1, meaning that a1 was previously vacant.

The last two moves were ...Ka2 (from a1) by black follwed by Na1 (from b3) by white, which incidentally is a really bad move that stalemates black -- especially when Ra1# was available.

Hmmm, on second thought, it's harder than I thought -- how did black's king get to a1 with that rook there?  The Ka2/Na1 sequence had to have happened earlier before the rook and king moved in leaving the only possible last move to be Kxc1 (a black knight, as it's the only peice that could have gotten in there without driving the black king away).  Also a bad move, as Rxc1 avoided the stalemate....

Do we know for certain that white started on this end of the board and not from the other? 

It's on the side with a1, therefore it is the white side and the pawns haven't moved.

Colegreen, Scarjo and Dr Doc MD solved it, nice work guys!

well is that true?

nice one, scarjo

hey that is 21 posts you have tiger13 in the 25 min. or so, are you trying to get some points ? if so why not start a forum of your own ?

Kxc1 white

In problems like this one you need to specify the full last move. Stating that you made a capture is not enough, What did you capture?

Per post 8:

I believe adding a white pawn to e2 forces the last moves to be Nd3-Nc1 followed by Kxc1.