Krakia?

The continent never sunk anywhere, for one thing. All the people in the mansion are either ghosts from way back when Olde Sappe existed and the mansion was at its prime or they were preserved for years. They haven't left the Mansion since Masteria reappeared, they don't know about the fact Olde Sappe was destroyed and a new city was built on top of it.

No.

I thought Masteria sunk and when it reappeared a thousand years later, Slimm had decided to build NLC over the remnants of Olde Sappe. Pretty sure it was stated that NLC sunk underwater somewhere, I just can't cite this anywhere.

Yes.