Something I played with for a similar setting was to make airships a lost technology. Mine were magically powered by big crystals, and the major island that was the source of mined crystals had fallen to a demonic incursion. The fall was recent enough that the tech was still mostly understood, but there were no longer any functional airships. I paired this with some floating Islands, like the ones from Avatar more or less. That provided some natural gating for the sandbox, because getting to the sky islands could only happen after an expedition to the demon isle to acquire another airship crystal. There was some long-arc stuff pointing to the Sky Islands as important, so there was a kind of natural teleos to the adventure.
I'm more into airships as an emerging technology, but I am also biased against lost technologies in general. But otherwise, I like the idea of travel to the sky islands being limited and hard, and airships being something to aspire to and work for.
- I could see a nation of water nomads using caste-ships and watchtowers-ships (like the Japanese atakebunes and other fortress ship), with a Louis XIV style court and sea-horse knights, pompous court traditions.
- Maybe a nation of coral growing architects, like the Telvanis from TES: Morrowind, but with corals instead of mushrooms.
Love all of that. I have an idea for psuedo-French Eladrin from a place called Capet (after Hugh Capet, the first "King of France", as such).
Even without a formal authority, there would probably be a lot of trade going on in such a setting, and a few big cities that are the hubs of that trade. Those cities would probably be wildly diverse - Star Wars cantina diverse - whereas most islands would probably have really only one race.
On the other hand, one island per race is also a good idea, just to keep it form getting too confusing.
I prefer to keep cultures insular, but have regions and archipelagoes have a decent amount of exchange.
As for trade, yeah for sure. No need for the "even without formal authority", since trade didn't rely on such things for most of humanity's existence IRL.
I would look to Indonesia, Polynesia, and the Caribbean for a lot of the themes you desire. Maybe throw in a dash of the Phoenicians, who were great sailors, but not island based.
Also, the Homo floresiensis are a good way to shift some of the familiar halfing tropes a bit.
Yes! I actually have done this a bit before, and would almost certainly play with this more in such a world.
I'm a huge of fan of Ursula K Le Guin's Earthsea, which offers a lot to draw from.
Yeah, you know I might as well reread those books before starting such a campaign. It's been almost 20 years.
No metal armour. Giant birds that spend 99% of their lives in the air. Migratory fish and sea mammals, and sea nomads who follow them. Floating islands. Islands on the backs of turtles. Icebergs, with frost giants. Underwater volcanos with fire giants. Merfolk giants. Babel fish. Intelligent ships. Anything you can steal from Earthsea. Sea elves that farm schools of fish. Sea dwarves that mine underwater volcanos. Sea halflings who don't go beyond the shallows. Halflings who ride albatrosses. Living storms. The great gods Rey-Dar and So-Nar. Gremlins that mess with ships' rigging in foul weather. Ghost ships. Ghost airships. Giant sea otters that float on their backs and dispense wisdom. Sea druids. Pearls as the dominant currency. A world that's never seen soap lather...
Lots of stuff here! Nice!
Why would the world have never seen soap lather? There is fresh water on islands, for one thing. For another, there are potassium based soaps that do lather in saltwater.
I wouldn't go with no metal armor, but I would encourage and engage in heavy reflavoring of armor and weapons in terms of materials.
Are you familiar with the game Archipelago?
Nope but I'm gonna check it out!
If there will be no humans in this campaign, you should probably figure out what merfolk look like from the waist up.
Abe Sapien, from Hellboy.
Another thought on gating. Here's how I approached it in the archipelago campaign I did up. To start tier one the party doesn't own a ship, too expensive, so they're reliant on the narrative to get them from place to place.
I prefer to allow small fishing boats and the like at starting levels, but otherwise yeah, makes sense.
My question, what adventuring opportunities to you envisage? What sort of quests would the PCs embark in that would take then from their village? Where’s the conflict?
That depends on the players, which is why I want a lot of ideas from people other than myself.
But! Here are some ideas;
- Dragons returning! True Dragons, Great Dragons, Wyrms, whatever you call them, the terrible beasts of the ancient tales are waking, and the world will tremble in their shadow. These dragons are something more than the metallic and chromatic super-mortals of vanilla dnd. These are more like primordials or titans. Beings so ancient and elemental that a single one can be an entire adventure locale. A standup fight with one is Epic level stuff, but an adventure that starts at level 1 could involve discovering that if the Dragon Atracraxis awakes, the island chain you grew up on will be destroyed, and take you all the way to level 5 as you enter ancient places and discover that they are part of the Dragon's body, and solve the puzzles and find the objects and perform the tasks required to return Atracraxis to her slumber, only to find out that another Dragon from the deep has risen, and now you must go all Shadow of The Colossus on the thing, because you're the only people alive who have explored the body of a living primordial dragon.
- Casablanca. Bends the "no empires" parameter, but keep the empires fairly localized and it's fine. You're locals, or adventurers, archeologists, deserters, whatever, and you're in a city poised between two powers, one rising with terrifying speed on the back of a great war machine, the other crumbling after a terrible defeat by the first in the land of it's very capitol.
- The princess must escape her homeland to survive, and has stowed away on your ship in order to do so. (Final Fantasy 9 ripoff, basically)
- The Omens speak of your destiny, and a coming storm that you must face. An old god rises, long thought dead, and only those born under a certain sign can defeat him. You must go into the wider world, and find both allies and legendary items, before it's too late.
- A conspiracy, itself the legacy of mistakes made by your collective parents, has come home to roost. The spring festival that brings together the people of the entire island chain is interrupted by the agents of this conspiracy, and the children of those targeted need to come together to find out what is going on.
Tarasques as giant-whale-behemoths with portal to the elemental plane of water in their mouth; they can swallow a whole island and send it to the water plane to be ''digested''.
Edit: Bonus idea: Why not have a watery Nine Hells instead of a fiery one? With a Davy Jones themed Asmodeus, if you go that way!
I mean, deep ocean volcanic terrain with rivers of lava or sulfur or mercury, with great heat vents turning the sea into bubbling steam...pretty hellish.
Not sure about the Tarrasque, but that sounds like a reworked astral dreadnaught to me! Sounds like an awesome take on The Leviathan.
I think the first question you need to answer, even before you think about the intelligent inhabitants of the islands, is decide what to do about aquatic humanoids. They have the potential to change the setting greatly because they aren't broken up by the islands.
You could have none of any type.
You could have them all part of a huge, diverse empire, that generally simply ignores land-folk and their clumsy ships. Apart from maybe taxing them or charging tolls for ships perhaps.
You could have them embroiled in a huge war between undersea nations, and so generally leave the land-folk alone because they don't have resources to spare on them, and they can't contribute. Perhaps they trade with island-folk for metal weapons and equipment, or perhaps they even keep captive populations on islands mining and smithing for them.
They could have diverse and individual populations of them scattered around just like the island-folk. - In which case, why are they sparse and scattered? Are they confined to undersea islands, separated by the vast blackness of the deeps? Or are there other dangers of the sea that keep the sea-folk from spreading out?
I don't think scattered populations need much explanation. The sea is
vast, with an exponentially larger diversity of creatures, both food and predator, than on a landmass.
Maybe there is an actual "life-cycle" of the races, where undersea islands slowly rise, and the sea-folk gradually adapt into land-folk. Almost all the populations of the islands used to be some race of sea-folk originally. Or maybe the other way around, and an island gradually sinks. The original land-folk change into sea-folk and then into the mysterious deep-folk which are hardly ever seen by surface-dwellers.
True or not, this could certainly be part of the setting's mythology.
Dwarves could be great ship-builders, whose floating fortresses slowly roam the seas, gathering resources for great expeditions mounted to find their lost homeland.
Or they could be a race of island-folk who live on volcanic islands - sensitive to the trembles of the rock below them, experts at building stone defences to redirect lava flows, resistant to noxious volcanic gases, and cunning at knapping tools and weapons from obsidian.
Okay, I love dwarves on volcanic islands to the far south, where the lava flows meet the glacial ice.
Gnomes could lurk in islands so densely-forested than only a creature of their size could move unimpeded. Ship crews that stop at their islands to harvest coveted fruits are oblivious that the crops are farmed deliberately to attract them - and their ships full of rats that the are used to communicate with gnomes on other islands.
I like this. Definitely not my only take on gnomes for such a setting, but for sure one I like a lot.
Tabaxi are a dying race. Their fondness for living on islands with tall cliffs is not suited to their instinctive propensity to push things off them.
You and I may have different inclinations wrt silliness in world building.

I'm actually tempted to use Leonid and Tabaxi as Greek and either Roman or Persian influenced cultures, having physically similar people sharing regional waters and having both trade and conflict in the more Mediterranean influenced region.
Halflings are still a chubby, cheery folk, living restful if short lives on their farms, kept safe from outside forces and steadfastly ignoring unpleasant matters. Such as that every so often, dark shapes arise from the waters around the halfling farms, and harvest some of the crop . . .
lol I don't love the halflings as blissfully ignorant shirefolk trope, but it is an entertaining thought.
My own take on them would probably be to put them in the shores and on Polynesian style catamarans, or something like that. Maybe work out a subrace with a swim speed and the ability to hold breath for much longer than others, but not breath water, and be acclimated to diving deep in the ocean.
Island dwarfism is very common (less nutrition sources means smaller critters are more likely to prosper). I'd say that should put Grungs in an exalted position. Perhaps gnomes and halflings can be pretty well-established in their own places.
I can definitely see a really wide variety of cosmetically distinct grung, with skin toxins that are mechanically the same but in world are very distinct, and it might be fun to do the same with gnomes or halflings, as well. Maybe switch out forest gnome cantrips island to island.
Also, reflavoring small races in some places as dwarf populations of other peoples could be fun, but has some unfortunate real world tropes attached.
real world island nations tended to be collections of villages (500 people or more) with a shared language and loosely shared beliefs, but pretty different island to island and village to village. This allows a great scene change with every stop, but common currents running through. Probably the same dieties or overlapping ones, but slightly different depictions and rituals.
This sort of diversity in a (compared to continental peoples) relatively small space is exactly what I want from an islands game.
Just like Maui is an important figure from Hawaii to New Zealand, with most of his traits and stories being very similar throughout, you can have hundreds of localized cultures over the span of hundreds of miles who revere and tell stories of The Raven Queen and how she tricked the old god of death into giving her his name and then killed him or commanded him away from the world or other fates varying from island to island, and hid her name where no one could find it so that she could never suffer the same fate.
Islands are places of strict competition for resources, particularly, islands which are inhabited by two or more villages which feel themselves distinct. Sentient lives are a very valuable resource, and a big investment. The party might find a village very welcoming but then expect a lot in return.
Sure, and you'll have different responses to those tensions. Some will have strict and/or byzantine rules of hospitality, others may be essentially socialist, others may raid outsiders, etc.