These alternate seas always feature a vast expanse of some material which resembles or functions like ocean water (or in the case of space, a vast expanse of nothing). Often there will be some method of traversing this landscape in a boat-like vessel or vehicle. These craft may be airships, wind-powered sleds, hovercraft, magical floating frigates, or some other ‘ship’ fit for this environment. These boats may need a harbor, so consider what settlements exist on the ‘coast’ of this sea (and what defines the coast in the first place). There may also be islands within this sea, so consider what terrain features or other elements may take on that role in your own world (mesas, asteroids, floating rocks, etc.). Along with frequent travel there may be trade routes, and expensive trade goods means there may also be pirates and piracy (or pirate treasure and treasure maps).

Pirates are not the only dangers that other seas commonly contain – many of these landscapes include their own forms of leviathans and treacherous seas. Massive storms and whirlpool-like phenomenon may also pose a threat to those sailing these ‘waters.’ And if including dangers such as these, it may be worth it to consider shipwrecks or whatever may be your worlds version of a wrecked vehicle. There may be lighthouses to help minimize the dangers or shipwreck towns full of the less fortunate.

As for the people that live in these regions, they may be sailors (or the fantasy world equivalent), fishermen, lighthouse keepers, or other working people or tropes that fit with a more oceanic world.