Cassedega is actually two cities, one above the water and one below. They were created on the ruins of an ancient city lost to the deep, and recently resurfaced. The new communities live in the rubble of the old and make a living delving into the ruins.
This is the initially commissioned greyscale version of the city map that was created for Sunken Empires by Open Design It’s definitely worth checking out. I did a Q&A on the map for the guys at Kobold Quarterly. It can be found here. This is rights reserved.
This is currently on show in the Terra Incognita gallery show at the Soho Gallery for Digital Art. The print listing can be found here.