"여우가 공원으로 돌아와요."
Translation:The fox returns to the park.
I was expecting the word for "park" to have some kind of suffix to denote that it's a location part of the sentence (something like -에 or -에서)
으로 acts as such. It means toward or to. The fox isn't in the park, doing anything in the park or coming from the park, he is on his way to the park. If it had 공원에 it would be the fox comes back, in the park, meaning he was already in the park and going back to something in the park.