I have a river behind mine. There was already one there naturally but I moved it closer to the back of Resident Services to make more room on the other side. There's just enough space for the villagers to go behind the building to go fishing. As well as a couple flowers just so it isn't bare grass.
I stuck a diner back there It's been there pretty much since the beginning, but it's apparently evolved to serve more and more different types of foods as the months have passed!