What is this area in the Realm of Torment?

I can't quite figure out what this area is (blue circle), all of the areas are in the place they should be except for the last Mission as I couldn't seem to figure out where it went (pink-ish circle). You can see it clearly from the Gate of Secrets but I have no idea where it is accessed from : / Anyone know where it is?

The last mission (pink) is on a seperate map. It doesn't fit in there anywhere. The missing town (blue) is presumed to be the entrance to the uncompleted elite mission, but nobody knows for sure.