To happen to pass by or go past a place; to come across a location by chance while passing.
駅の前を通りかかると、昔の友達に会った。
When I happened to pass by the front of the station, I met an old friend.
散歩していると、ちょうどよいパン屋を通りかかった。
While walking I happened to pass by a bakery that looked perfect.
通りかかった人が事故を見つけて通報してくれた。
A passerby who happened to be passing by noticed the accident and called it in.