Yeah, I'd love to see what you have for it.
Much of this is shallow sea themed but....
The "island" of Moradin. Imagine the world's largest volcano filled with heavy metals (iron & adamantine). The mouth of the volcano was over 5 miles wide. It cools then becomes exstict. Now dwarves find it and begin to tunnel in it and creat a roughly round SOLID IRON island kingdom stronghold. Below it under the water (miles below) are gems and secret passageways to other lands that they only know.
Halflings
Floating city. Inspired by Waterworld. They float over sunken ruins and dive for treasure and resources. Then move on to the next one. Generally friendly and open as they do a lot of trade with other island nations.
The Fog
Everyone avoids this area as there is a thick fog bank HUNDREDS of miles wide. The water is much deeper. Strange lights and flying crafts are seen coming and going. Boogieman tales run rampant involving the people / creatures that live here.
This was my "Epic" level area. Gateways to other dimensions are located here along with the Hall of Fallen Heroes. A massive floating island with a permaneant gate to the water dimension. So near the top is a palance surrounded but a float that branches out to other levels. Each level is connected by this "water drainage" system until it finally "rains" below into the fog. This makes the fog even more dangerous as the water is always choppy and there are waterfalls seemily crashing down from no where.
Mangroo Sea
Mangroo are a type of bush/tree that grows in florida. The roots lift the tree out of the water creating mazes on the surface and dangerous mazes below water where aquatic creatures lurk. This "sea" is again 100's of miles wide. No one going in has ever left. This was to be my high level area.
Everywhere under the sea were Sahguine cities. Some good, Some not. There was constant battles and most of the time no one ever knew about it. There is a new king for the "good guys" that wants the surface world to help him. This is creating trouble as many of his subjects don't want the surface involved. The bad guys are spreading bad rumors about the surface and are also recruiting powerful forces from the surface.
Golem city
Warforged basically. It was where everyone was a mage that built things (House Cannith) including their speciality- Golems. And many were treated as family pets given limited intelligence. These "pets" were handed down from generation to generation as an heirloom might. Recently they have been created war-type golems but no one knows why or whom commishened the job.... or was it them themselves that are preparing for war.
Island of the dead-
Long ago it was where everyone buried their dead. It was neutral place from a much more peaceful and unified time. Now the island is full of hateful or at least distrusted undead that are trapped on the island. However there many secrets on the island...including how to lift the restriction of their imprisonment.
any more? These are from the top of my head. I have notes that I began to unbury when cleaning the hobby room.