階かい段だんを上あがる

expression, godan verb (-ru)

go up the stairs; climb the stairs

Common phrase for ascending stairs. 上がる is used here as a transitive verb with を, meaning to move upward along the stairs.

• エレベーターが混こんでいたので、階かい段だんを上あがった。

  The elevator was crowded, so I went up the stairs.

• 彼かれは一いっ気きに階かい段だんを上あがってきた。

  He came up the stairs in one go.