I'm not sure I can picture what it means to be "behind a street." Would that mean it is on the next block over?
Yep. something like that. When you look at houses (or whatever there is) in this street, the castle is just behind these.
I like that. We tend to think of the street itself, but Hebrew, like a lot of other languages, clearly sees the buildings as part of the street. Actually, British English may do this as well.
cant "מאחורי" mean after? So like, after we pass this street, we will see the castle-type thing?
after is אחרי acharei