V. + ㄴ/은/는 + 것이 아니라 => "it is not (the fact) that," "not . . . but . . ."

This expression amends the action, event, or item in the first part of the sentence by the second part.

• 고속 버스를 타는 것이 아니라 기차를 탈 거예요.
  => We are not taking an express bus, but we will take a train.
• 여기는 날씨만 좋은 게 아니라 사람들도 친절해요.
  => Not only is the weather nice here, but the people are also nice.