Cassadega 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 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.