"the back"

"Let's go around." means you could be anywhere by a certain place and the "around" is anywhere in a half circle kin of. "Let's go around the back." means you are in front of a certain thing and you want to go behind. And it basically means with "the back" part is you are going in somewhere. If you would have said, "Let's go around back." means you are more general about where you are going but you are still going behind. ***You can replace "back" with "front" too, only if the situation is reversed. Hope this helps^^ Have a nice day!

I suspect that "go around back" is more American & "go around the back" more British, but I could be wrong. ......Actually in spoken language "around" is very commonly used where "round" should be.

You would actually say, "Let's go around back" The first sentence is really incomplete, and the second one does not need the definite article. Brian