Actually, it's unlikely they swapped it with mog house, according to a friend of mine. He said the mog house position (0 0 0) is inside of a wall in Al'Daahzl Undersea Ruins.
He, being the stupid DRK he is, swapped it with Al'Taeiu, so he died quite a few times to sharks hiding under the floor.
Anyway, if you look at tinypic, there's exits to Mire AND Thickets, and it looks like those towers you can see off the ship to Nashmau. In my opinion, this is probably related to those Immortals who stand in front of the tunnels we can't enter. Though, there is an area called "Testing Area" near the COR Quest Cove, which goes to a gate, which is (as far as I know) unable to be opened.
But yes, this area does seem to go completely underwater, since it's connecting Thickets and Mire.
If anyone cares to see a pic of my friends model swapped adventure, it's here
http://i3.tinypic.com/zjcu84.jpg