I keep a folder of images just for this. Trolling ArtStation for stuff that could potentially work in the League Universe is like a part-time job for me.
Nerizameth is a part of Ancient Shurima, it was the first capital of Shurima and was where they built the Sun Disc that would later hover over the new royal capital. Ironically, even though as a man Xerath was a slave campaigning for the rights of all other slaves, after he becomes Ascended I imagine he no longer holds on to these ideals of self- determination and free will
Driven insane with power, he now seeks to take what he believes is rightfully his and replace the upstart civilizations of the world with one fashioned in his image.
Xerath sought the heart of the desert to regain his strength and understand how the world had changed in the millennia since his imprisonment. His stolen power grew with every passing moment, and he beheld a world ripe for conquest, a world brimming with mortals ready to worship at the feet of a new and terrible god.
Much like the Ascended beings and Darkin before him, Ascension has came to make Xerath see all other mortals as little more than cattle so its hard to envision Nerizameth as anything other than an empire built on the back of slavery. I think it's a good way to sell his turn to villainy, watching him lose his one redeeming quality and truly lose himself to his thirst for power that he developed ONLY because he was a slave for so long. The oppressed make for the best oppressors.
https://i.ibb.co/PwDKxq0/Nerimazeth.jpg
Nerizameth should be more drab, because this is before Shurima ever got involved with Targon and before they had an Ascended army that let them conquer the world, flooding the imperial coffers with gold. Its a dark depressing place.
As a bonus that image is actually drawn by an Artist who draws for League all the time so it matches the style for the other stuff he drew like Targon his name is Gabriel Yegeyemon
https://www.artstation.com/gabe-11
https://i.ibb.co/rGsyPGm/pablo-dominguez-2017-kayframe1-slaveescape.jpg
Here we can see the extent of the slave labor.
https://i.ibb.co/WV8vPSf/pablo-dominguez-2017-kayframe2.jpg
And a sweeping shot over the whole empire so you can see the whole scale of it.
These are by the talented Pablo Dominguez he did a lot of concept art for Captain Marvel and even worked on Game of Thrones
https://www.artstation.com/pablodominguez