I feel its Hraesvelgr's lair; or part of it anyway. Its just too close to Zenith (in location and style) and has Dravanian Motes in it (which means the Moogles had a hand in it as well)

Sad Apology...Hraesvelgr mourning what happened to Shiva, what Thordan did to his sister, what he did to start the War (face it, if he didn't save Nidhogg the war never would have begun). Maybe intended as a memorial to all that was lost in this conflict...

But then...why are we there? Nidhogg's brood attack it? We're attacking it to get to Hraesvelgr to get him to help stop Nidhogg? Echo-trip to the past to find a way to save Estinien?

Hm...going with the Echo...what if we go to Hraesvelgr to try to get him to help stop Nidhogg/save Estinien, he gets us to Echo to this place 1000 years ago for something important...his way of apologizing for his part in the war...