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 was created for Sunken Empires by Open Design [link]
It's definitely worth checking out. This is rights reserved.
This is currently on show in the Terra Incognita Gallery Show. You can find the print listing here: [link]