Telegraphing Black's intention to play ... f5. White will be ready for it.
16. g4 Qd8h4
This looks aggressive, but the lone Q will not be able to stir up any trouble here; White is adequately defended.
17. Bc1d2 Bg7d4 18. Kg1g2 Qh4d8
The retreat is forced, as White was threatening to block the Q's retreat with g5, followed by Be1 trapping her. Note that the three White pawns on a5, d5, and f4 are completely paralyzing Black's knights.
19. Nc3e4
With Black's Q-side plans effectively blocked, White now migrates the QN towards the K-side to take part in the coming K-side attack. The text move accomplishes this strategic maneuver by offering to trade White's low-value b2 pawn for Black's high-value d6 pawn.
19... Nc7e8
Black wisely declines the offer. However, the Black N on e8 further restricts Black's mobility, effectively preventing him from occupying the e-file and burying the Black KR.
20. c3
Booting the Black KB back where he came from. Black's position is already almost untenable, due to space constriction.
20... Bd4g7 21. h4
White now bears down on the Black K-position. A breakthrough is imminent. Of course, ... Qxh4 is suicidal, as Rh1 forces the Black Q to retreat (again) and then White doubles rooks on the h-file.
21... f5
Black desperately needs to gain space to manoeuvre in. However, ...
22. Ne4g5
with ... f5, Black lost control over the critical square e6, which White now targets.
22... fxg4
This exchange is not good for Black, as it opens the h3-c8 diagonal for White. But what else to do? White was threatening to invade the Black position with Ne6, and open a file to the Black K with h5 as well. 22. ... Nc7 to hold the e6 square would be met by 23. Ne6, Nc7xNe6; 24. d5xNe6, and the N on d7 is lost for if ... Nf6 then 25. e7 dis+ wins the Black Q.
