To go out for fun or to visit someone casually; to go to play or drop by a friend's place.
週末は友だちの家に遊びに行く予定だ。
I'm planning to go visit a friend's house this weekend.
子どもたちが公園へ遊びに行った。
The children went to the park to play.
ちょっと近所へ遊びに行ってくるね、夕方戻るよ。
I'm just going out nearby for a bit; I'll be back in the evening.
休みの日にはよく祖父母の家へ遊びに行く。
On my days off I often go to my grandparents' house to visit.