Icebergs
There was a thread on TwitterX recently advising writers to only worldbuild things that would appear in their book, and nothing else.
If that works for you, I guess go forth and do so. But its exactly backwards as to how all the Galhadria products work.
Example: the Vigabrock II RPG adventure module is in progress. It’s set near the city of Eriad, in the Eriadan Reach (the region is named for the city, of course). The current settled area of Eriad is a small fraction of the entire city. Once it was home to a large gathering of giants who wrought an amazing city of stone by the shores of a deep, clear lake. Those giants are long gone now - dead or moved on, nobody seems to know. What’s more, there is a second city that the denizens of Eriad can see beneath the water when they brave the lake to catch what fish don’t catch them - ruins. Ruins everywhere. Ten times as many ruins as there are buildings still dwelled in.
That’s just one city in one region of one kingdom on a whole continent. There are reasons, layered into the ancient history of Nova Eian as a continent and Galhadria as a world, as to why those ancient giants built such a grand city, and why they moved along, and why the place is a ruin now. Exactly zero other stories have been set in this particular spot, but I did the worldbuilding for it anyway, because it’s a place that exists in the world.
This contributes to what we call the Iceberg theory of story writing. What makes it to the page is 10% of the lore of the world - the part visible on the surface. A story might take place in Caladel, far away to the south, where sailing ships ply the great harbor and pour one out for the Kraken - but Eriad’s ruins still exist, far away in the cold north, and might, in some sublte way, influence a story set in another place at another time. An artifact in a shop. A rune staff carried by the local wizard. A painted shield. If we haven’t done that worldbuilding, those details won’t exist - or, if they do exist, are created on the spot and, untethered to a greater story, will be forgotten or scattered to the wind because they have no attachment to the rest of the world.
So, do what works for you, but as for me - I’m going to keep building icebergs.