Bridges

You can always build a long room in the place you want the bridge to be, put floor tiles on the roof and a fence surrounding it, then remove the room underneath and only keep the roof as a bridge. Of course, that means the bridge will be as high as a room, but maybe you can do the same thing with a foundation? Or edit the terrain surrounding the bridge to make it look less high.

I can't try it right now because I'm not at home, but I imagine that's more or less how it works.