Forgot some lore elements from ARR and Heavensward and what's the shape of the world?

[BioDio]

Nero tol Scaeva disappeared at the end of the Crystal Tower arc, yes, presumably to pursue his agenda. He showed up in Heavensward at the Carteneau Flats during, uh, 3.4 or 5-ish, to hint at Omega.

Thanks! Everythings feels more clear now >_<
Just wanted to grab that quote, since this still makes no sense to me.

So, as far as I remembered, he stayed inside the Darkness Abyss.. or wtv was the name of that place, and it's impossible to get out of there, yet he did, is there any explanation?
Also, where is the Carteneau Flats in game? might sound noob, but I don't recall going there.

So basically, since the end of the Crystal Tower, or Heavensward, he's been looking for Omega?