Meisterwerke

The position unlocks when black can retract a6xb5. For this, the white knight from c7 needs to unpromote on a8, and the pawn should go back to a5. This means that a black knight on c7 is needed to prevent a check by the white bishop on b8. This means that the white king should go to f8.

The retro-play is: -1. ... Nc8-a7 -2. Ba7-b8 Nb8-d7 -3. Na8-c7 Na6-b8 -4. Nc7-a8 Nb4-a6 -5. Na8-c7 Nc2-b4 -6. Nc7-a8 Ne2-c2 -7. Na8-c7 Ng4-e3 -8. Nc7-a8 Nh6-g4 -9. Na8-c7 Rg8-g7 -10. Nc7-a8 Rh8-g8 -11. Bb8-a7 Ng8-h6 -12. Ba7-b8 Bh6-f8 -13. Bb8-a7 Bg7-h6 -14. Ba7-b8 Bf8-g7 -15. Na6-c7 Nh6-g8 -16. Nb4-a6 Ng4-h6 -17. Na2-b4 Ne3-g4 -18. Nc3-a2 Nc2-e3 -19. Nd1-c3 Nb4-c2 -20. Ne3-d1 Na6-b4 -21. Ng4-e3 Nb8-a6 -22. Nh6-g4 Nd7-b8 -23. Ng8-h6 Bh6-f8 -24. h3-h4 Nf8-d7 -25. Nh6-g8 Rg8-h8 -26. Ng4-h6 Rh8-g8 -27. Ne3-g4 Bh6-g7 -28. Nc2-e3 Rg8-h8 -29. Nb4-c2 Rg7-g8 -30. Na6-b4 Nd7-f8 -31. Nc7-a6 Nb8-d7 -32. Kf8-e8 Na6-b8 -33. Na8-c7 Nc7-a6 -34. Bb8-a7 Na7-c8 -35. h2-h3 Nc8-a7 -36. a7-a8=N d4-d3 -37. a6-a7 Na7-c8 -38. a5-a6 a6xBb5

and finally the position unlocks. Very surprising and hard to find tempo-maneuver with the black bishop!

Solution by Henrik Juel