There is a planet in /mysector/ called Bastio. It's a water world with moving, floating hive cities. And for some reason they have insanely good laser tech and can provide laser destroyers to nearby factory worlds. It's a little different from normal hive cities because the lower the level, the more prestigious and wealthy the residents. The surface is fairly flat and highly radioactive. The aquatic life is monstrous and mutated. Pirates and such attack constantly (think Waterworld) and giant bunker buoys from lower levels shoot out of the water to fend them off kilometers from the hive. The mid tier levels have flooding and severe gang warfare (think bioshock). They either fight aquatic horrors, mutants, or each other. The lower levels are dry, brightly lit, and secure. The rulers of the hive live here. Pomp and circumstance, possibly fish people, etc. They'll often open an airlock, let a horror beyond belief run rampant in the populous, and hunt it down to 'save' the people and reaffirm their loyalty.

There is also a feature that all hives on the planet have. A giant tube running all the way down the hive. A lot of people have moved into the tube for various reasons. Entire cities have been built (think favelas lining a giant missile silo) in the tube. Billions of people. The tube is an anti-orbital laser weapon, which is used in my lore. The first shot atomizes everything in the barrel and doesn't perform like it should, pissing a noble off. Turns out all those people and structures reduced efficiency by 15%. He scoffs and fires another shot.

There are subnautical knights fighting off cthulus, guardsmen in "Fathom Armor" similar to big daddies patrolling the levels, mutant shark people rampaging, etc.

Just one of many planets somewhat fleshed out.