Breaking into the opponent's castle

In this following game lichess.org/study/gQDOgjxC I faced a common pattern which I never know how to deal with. At move 18, I choose to take the knight on f3, doubling the f pawns and opening the castle. Since I also chose the little castle, the g file of my opponent is now ready to attack my king with his rooks.

In this kind of pattern am I usually supposed to take the f3 knight? Or is the new open file strong enough to take advantage of it?

Your LSB was well placed on d4, why exchanging that valuable bishop for that knight? Keep the tension, let the opponent take and if he does, you would recapture with the knight and have a strong knight in the center.

Also, this should have been in the "Game Analysis" forum.

TLDR; Doubling pawns is usually good :)

@nico2del said in #1:
> In this kind of pattern am I usually supposed to take the f3 knight? Or is the new open file strong enough to take advantage of it?

The doubled pawn on f3 can be a weakness in the endgame:



But before the endgame there is the middle game, and here the double pawn will restrict your knight, and his bishop d3 feels more powerful. Though, it seems not to be a big advantage for white. Rubinstein probably would disagree.



I didn't check with the computer, but 18...Bxd3 followed by Ne4 and f5-f4 (black minority attack) looks like a sensible idea. Maybe also first 18...a6 to be prepared to exchange the a-pawn when he plays b4-b5 (white minority attack).