Ravnica

Therrik's home, or at least his first one. There seems to be a large underground society that he was a part of there, involving large intelligent insects called Kraul, as well as undead workers, Gorgon, and elves.
There's a group known as the Orzhov there, although Therrik could only tell them so much. Some of their old subterranean vaults had been taken over and "made beautiful" by his... people? He explained that the organization was run by angels, although he did not know of the one on Brian's list.