Nn6/8/6r1/8/K7/1P6/1R6/3k2N1 w - - 0 1
After white sacrifices the knight, the rest of the ending does border on being inhuman, but is understandable if you think about it. So, after 1.Kc3 Ra6 2.Kb4 Rxa8 3.Kc3 Ke1 4.Re2+ Kf1 5.Re8! Kg1 you have the winning position that can be verified by the Nalimov Tablebase. Whenever the black rook departs the a8 square, the black knight is lost at b8, so the ending is like a R+P vs R ending where the issue is not allowing the black king to close in on the upper left corner of the board. White must use the king to help his rook accomplish this, but the white king will have to be careful to not allow black to play a check from the a-file while preparing the right moment for the advance of b4.
White has to sacrifice the remaining knight.
As far as I see white mustn't let black win the white pawn so the only move is Kc3. I got stuck at the fourth move.
White's third move should be easy to spot.
Yancey,thanks to your hint I have found the two key moves.
I have no idea how to proceed next so far. It's a very challenging endgame for me. I will try to solve it.