Where would the heartland of the ancient Empire of the Visha have lain?

As of now, I've only completely read the Character sheets, but I see a lot of states formed from conquest following the fall of the Vishput. Given that, some stark contrast seems like a nice touch, so I'm looking at making these guys monks and scholars more than anything else. I'm debating between joining as a nation or just a small temple from which great historians come from. Whichever I make, I want this to have a flooded underground temple or city built from ruins of the Empire.

Any suggestions? What's a good place on the map given that? I'm working on the CS right now.