Meisterwerke

Black captures are axb and bxc. Either one of these captures is the white e-pawn, or this pawn promoted and is still on the board. In both cases, this pawn had to promote, since there's only one capture left (axb and d6xc7 are the other two captures). This pawn had to capture a piece on d7. To unlock the position, black needs to retract d7-d6, after bringing his bishop (which has to get uncaptured) back to c8. The whole cluster on the left of the board was already completely on its place when black played d7-d6, so the promoted piece is still on the board. The only piece that could've escaped from d8 is the queen on f2. To prevent this queen from giving a check, when it was on d8, a screen is needed on c8 or b8. The only piece which can give this screen is the white king. It entered the 8th rank via h6 and g7. So white may not castle.
1. Kd1 Ra3 2. Kc1 Ra1#.

Solution by Philippe Schnoebelen