Castling helps to build a strong fort around King

Castling is a special feature of a chess game and the idea behind is to keep the King in a fortress so that the opponent has a tough time in infiltrating and invading. Castling can be done on both the King side as well as the Queen side, though the King side is the most favoured one.

In the game which follows, Black has an opportunity to castle on either side but wrongly decides to castle on the queen side.
There after White unleashes a terrific attack, starting with a knight sacrifice. The Black King then tries to flee back to the King side but White’s pieces stop him in his tracks.
White: Alexei  Fedorov (2659) – Black: Vlacheslav Dydyshko (2521)
Aars, 1999 The Sicilian defence
1.e4 c5 The Sicilian defence
2.Nf3 e6 3.d3 d5 4.Qe2 This was the trend in the nineties.
The usual continuations are 4.exd5 or 4.c3
4...Nc6 5.g3 Nf6 Black can also think about 5...Be7
6.Bg2 Be7 7.0–0 b6 If 7...0–0 8.e5 Ne8
8.e5 White also had 8.Bg5 at his disposal
8. ..Nd7 9.c4 d4 10.Nfd2If 10.Ne1 Bb7 11.f4 Na5 12.Nf3 Rc8 13.Nbd2 a6 14.Ne4 b5 15.b3 Qb6 16.Bd2 0–0 17.g4 and White is better  
10...Bb7 11.f4 Qc7
12.Ne4 a6Black played a new move here.
Interestingly Black had the option of castling on either side in this position.
If 12...h6 13.Na3 a6 14.Nc2 b5 15.Bd2 b4 16.b3 a5 17.a3 0–0–0 18.axb4 axb4  
13.Nbd2  
Diagram 1

13...0–0–0 Perhaps castling short appeared a better option at this point.
14.a3 h6 15.b4White advances on the queen side
15. ..Kb8 Black could have tried to force things on the King side with 15. ..g5 or 15. ..h5. If 15...cxb4 16.axb4 Nxb4 (16...Bxb4 17.Ba3) 17.Ba3.
If  15...f5 16.exf6 gxf6 17.bxc5 Bxc5 (17...Nxc5 18.Nxc5 Bxc5 19.Qxe6+) 18.f5
16.Nb3 Ka7 If 16...cxb4 17.axb4 Bxb4 18.Ba3  
17.Bd2 Ra8 If 17...f5 18.exf6 gxf6 19.f5 and White stands better  
18.Rfb1 White had a better continuation in 18.b5 Nd8 19.bxa6 (19.a4 a5) 19...Bxa6 20.a4  
18...f5 19.exf6 gxf6 20.b5White missed a good move in 20.bxc5 bxc5  21.Nxf6 Rac8
20. .. Nd8 21.a4 f5 If 21...a5 22.Nxa5 bxa5 23.b6+ Nxb6 24.Bxa5 and White is winning  
22.a5White sacrifices the knight to open up the gates towards Black King
22. .. fxe4 23.axb6+ Nxb6 24.
Bxe4White has sacrificed the knight and is now trying to catch the vulnerable looking Black King into a checkmating net
24...Kb8 25.Ba5 Kc8Trying to flee in urgency?
However Black could have tried to offer better resistance with 25...axb5 26.Bxb6 Qxb6 27.Rxa8+ 26.Bxb7+ Qxb7 27.
Qe5White is totally dominating now and is winning.
White can also win with  27.Nxc5 Bxc5 28.Qe5  
27...Rf8 28.Nxc5 White’s pieces are now intruding and invading
28. ..Qa7 If 28...Qb8 29.Qxb8+ Rxb8 30.Nxa6 Rb7 31.c5 and White is better  
29.Nxe6 Nd7 If 29. ..Rf6  30.Nxd8 Bxd8  31.c5 Nd7
30.Qe2 Rf6 Black hardly has any good moves at his disposal.
If 30...Nxe6 31.Qxe6 Qc5 32.Bb4  
31.Bxd8 Bxd8 32.Rxa6 Rxe6 If 32...Qb8 33.Rc6+ Kb7 34.Qe4  
33.Qxe6 1–0
Diagram 2
White to play and win
1.. f3+ 2.Kg1 If 2.Kg3 Qxf1 3.Ne3 Bd6+  
2...Qxf1+ 3.Kxf1 Rd1 check-mate.