Wonderful thread! For my own use I copied down all the questions to contemplate for my story. I thought others might like it too.
What is the most valuable substance in your world?
Who is the most dangerous person on your world?
In your world, what do people eat while on the road?
How common is sericulture (silk-making) in your world, and what is it used for?
How well-understood or well-researched is the most unusual phenomenon in your world (compared to real life)?
What place is there for an atheist in your world? How do other people react to them?
What's the strangest (and most incorrect) thing that people in your world believe in? Or vice-versa? What's something that's completely true, that people think is made up?
What do teens do for fun that adults don't approve of?
What is the primary mode of transportation in your world, and how do people "pimp their rides"?
How much has changed in your main culture between your protagonist's generation and their grandparents'?
What year is it?
Name me a popular in-universe piece of literature.
For your longest-running civilization... what is the secret to their success?
What is the absolute worst, most embarrassing faux pas an upstanding citizen could possibly commit? What social sin do people of good taste have nightmares about in your world?
If a character is frustrated, what's an exclamation they might shout? Are there are words/phrases that are socially uncomfortable, but people use anyway?
Question: are characters in your world able to hold a place of importance even if they are physically disabled?
How does an interesting culture in your world finance itself?
How is information and knowledge in your world spread and acquired?
Does your world have illegal drugs, or consumables which are taboo?
tell me an in-universe joke.
Does your setting have Wonders of the World? Taj Mahal, Angkor Wat, that sort of thing. What are they?
What's the war that people still talk about?
What sort of technology/advancements have your societies invented to protect themselves against an (by real-world standards) unnatural threat to their safety—either some kind of dangerous phenomenon or a monstrous and/or magical enemy?
Does your world have an afterlife (either believed in or real), and if so, what does it look like?
What major festivals do your characters look forward to?
Tell me about a group or clique in your world who is considered 'cool'.
What is the most important virtue for your MC's people? Strength? Loyalty? Cleverness? Or something else?
How does sanitation work in your world?
What does popular music sound like?
Are there slaves in your world, and how are they kept in line?
Back to the information, is there any fake news or other false information spreading through your world?
My question, what sexual kink is unique to your universe and why?
Tell me about the moon is your setting? Is is just like ours? Are there any interesting myths or bits of folklore surrounding it?
What plants are unique to your world/culture/kingdom? Do they have particular properties, magical or medicinal or cuisine? How have they shaped the cultures of your world?
What is the most horrible injustice or tragedy that is ongoing or has recently happened in your world?
What kind of art is prevalent in your world? Does it have famous artists? Is any of it banned or taboo?
Is tourism a thing? Is it developed? Is it dangerous? What are the things or places you must absolutely see before you die?
What is the technological level of your world? What is the closest comparison you can give?
What is universally regarded as the best wine & cheese combo in your setting?
Tell me about animals. Any earthlike species? Anything truly bizarre?
There was a question about music styles, but what's that one song in your world guaranteed to give its listener earworm, whether they want it or not? Is it culturally beloved or hated or both? Where did it come from?
What is a way (unique to your world) to win the Darwin Awards?
What are the naming conventions in your world? Tell me some of the popular ones.
How many different forms of government do you have in your world? Are they all hereditary monarchies? Elective monarchies? Is there a democracy, an oligarchy, a constitutional monarchy, and an autocratic Empire? Is anyone form considered to be better in-universe, or do they all have flaws?
What traditions among the people of your world have been abandoned, either largely or completely?
I wanna live on a mountain! Tell me about a cool one (and asteroids count as mountains, btw).
In your world, what is/are the most valuable thing(s) to trade in?
If I were to look up at the stars, would someone/thing be looking down on me? Spiritual, celestial, extraterrestrial or otherwise?
Are there utilities like electricity, heat, running water in your world, and if so - who or what produces them?
Tell me a famous urban legend. Not a grand myth, but more like a spooky story teens tell.
What’s the life expectancy?
What does poverty and wealth look like in your society, respectively?
Who's considered the greatest historical leader in your setting? Who's considered the worst?
What new advancement in technology has been introduced to your setting, and how is it changing the way people live?
What sorts of clothes do people wear?
What is the strongest and most notable feature of your world's environment that would interest the reader?
In what ways are social castes divided in your cities, aside from wealth?
What "truth" does everyone in your world know to absolutely be true, but isn't?
What are some deadly monsters/animals in yoru world? Or simply the deadliest, if you prefer.
What is the state of medicine in your world? If magic is involved, I'd love to know how that affects it, but would also be interested in more mundane techniques.
You open up a bestiary of your world to a random page, what is contained in the entry you've opened up?
Question: Do youths in your world have to achieve adulthood through a specific ritual or ordeal? If so, what? Or is it just "You're now 18. Go and have fun adulting!"
How does one become or know they are an adult? Are there any coming-of-age rituals?
What religions (if any) are prevalent in your culture, and if there is more than one, do they get along?
What kinds of animals does your society use both for work, and companionship? Any interesting livestock for food? Is there anything interesting about the way your society uses or relates to animals?
What lives beyond the edges of your map?
Are there sorcerers in your world? If there are, do they get paid for using their magical skills, and finally, if they are paid, how are they compensated?
What is the deity of your world, and what makes it unique from the modern religions of the real world?
Who is ruling your city/country/kingdom right now? Are they considered a good ruler? Tell us why the commonwealth likes/dislikes their leader.
Does your world have sports? Are they the same as ours or different? Is there a world championship?
Do people in your world believe in paranormal things (outside of religion)? Do some people believe their legends or tall-tales are true? (ghosts, bigfoot, etc.)
If your story centers on one country/city/settlement, who is their greatest ally? Who is their enemy?
Do people in your world use any weapons or transport different to that of Earth?
What’s the most common name? Boys’, girls’, gender neutral?
What is a period in your setting's history people look back on in shame? Were there any saving graces?
What are the various types of legal punishments for different crimes?
How do those in traveling professions—bards, traders, diplomats, etc.—serve as conveyers of ideas across different cultures in your world?
What are the standards of beauty that dominate the cultures of your world?
What is the exchange rate for your local currencies?
Does racism exist in your world? How did it get to the point it's at now? If there is no racism, how the heck did your awesome society mange that?!
If magic exist in your world, how powerful can it be? And what is the cost of a really great power?
You sit around a common setting with some of the everyday folk of your world, what sort of legends or fairy tales make up their oral traditions?
What's the fastest form of communication in your world? Instantaneous telepathy or messengers running miles a day?
What is the weirdest or most interesting lifestyle on your world? A priesthood with especially bizarre rituals? Merchants who strive to avoid either profits or deficit?
When a person of importance dies, what are the rituals and ceremonies surrounding the death? How is that different than the death of a citizen?
What is a day in the life of a member of the lower classes?
Tell me about your night sky. What are the constellations like? Any astrology or other such beliefs?
Where did civilization begin? What were the ancients like?
What’s a rude gesture?
How do music and/or dance factor into your world? What are some regional tastes or uses? Are there any societies that use them in ways that would surprise us?
What items are used for cosmetics in your world?
What's an interesting outfit or style of clothing? Ritual, celebratory, everyday wear, anything at all!
In your world, how do the people count the seasons? Do they celebrate the end of the year/calendar? If so, how?
What is the significance of dreams in the cultures of your world?
What are some of your favorite building, crafting or manufacturing materials on your world? They don't have to be special, just special to you.
Are there unique units of measure in your world? What's the standard measure for time? Distance? Volume? Weight?
What are some of the ongoing 'unsolved mysteries' or your world. Like, the Bermuda Triangle or Bigfoot. Things that may just be rumors, or have lurid urban legends surrounding them, even if the answer might be something mundane.
What are some really interesting landscapes from your world? Beautiful, stark, starkly beautiful, just peculiarly pleasant, historically significant or new and strange, your call.
What is the most abused drug in your universe?
Is justice in your world just? How so?
Are there philosophies in your world? Competing ideologies?
What's the main (or one of the main) styles of warfare on your world? If not full-scale war, the next biggest thing? If not violence per se, then what's the main form of conflict?
What qualities (good and bad) are most often found in your world's upper elite (rich, famous, heroes, celebrities, rulers, etc.)
What world/region specific curses or phrases are commonly used?
Who is the most well-known individual (or perhaps group of people) in your world? Why?
Free choice, talk about any worldbuilding subject you want, but it has to be written in the voice of one of the setting's characters.
How many cities are in your world and how do they differ from one another?
Do the peoples in your world aspire to better themselves, to advance their civilization?
What are some of the biggest social fouls in your world's cultures? You know, those things that you just don't do?
Describe two unique creatures in your world. One that is good or harmless and another that poses a threat.
What's a key field of science, technology, or study in your world? If you have magic, does it compliment, undermine or have no impact on this field?
Describe a palace your world has. Or at least a very nice building.
Does your world have any plants with strange or magical properties?
What's one of the most popular languages in your world, and what are some of its unique grammatical properties?
I love evil cults. Tell me about a nasty one.
Let's go meta! What's the role of literature in your world? Does it even have one? Go as big or small with this as you like--one author's works or the overarching literary themes of the entire planet.
What's the role of family in your world? How valued are parents and children and so forth?
Tell me about the health care system in your world.
Is cheating a social norm, or is it a terrible betrayal? Is it handled differently if a man cheats vs. if a woman cheats? How loose is your society, and what is considered unacceptable relationship?
What does the process of courtship look like in your world, if there is one? Marriage customs or traditions? Weddings? Etc.
Tell us about some fun relics from your world. They don't have to the geometrically-perfect weapons of a disappeared Elder Race--if it's really old and maybe just a little mysterious, that's relic enough!
How important are merchants in your world? Do they have true power and status, or do they make up a wealthy but socially scorned class (as in medieval Japan)?
What secrets do your world's governing bodies have from the people? Is there anything that could bring society crashing down if it were revealed?
Does your world recognize mental illness? Do they help people who are unstable? Or do they label people with cute names like 'mad hatters', or maybe discard those people altogether?
What are some big ol' rip-roaring celebrations in your world? Or little, charming celebrations, those are good too.
Tell me a story of what happens when people anger gods. Are there gods? Or merely the powerful who pretend to be?
Incarceration. How is it handled? Prisons aren't supposed to be fun, but are there any ways yours are particularly nasty?
How is sexual identity handled? Is it a problem? Is it accepted?
Think about the "Boss" characters from your work. What music would they have as their personal soundtrack, and why? You don't need to go note by note, but how does the song express the character and the world they live in?
When people in your world grow up, what is the most common dream they have? And how does it evolve as they grow up into the adult, real world?
What kind of role does Fauna play in your book? Do you have any magical or unique? If so describe them.
If your MC could change one thing in your world, what would they change and why?
What piece of technology would your world be lost without?
What's the main form of transportation in your world?
What is a public social service that everyone takes for granted in your world?
Describe a day in the life of an ordinary, working-class person in your setting. No one heroic or interesting.
What is a unique job or jobs in your world?
What are the fashion trends of your world?
What is the most dangerous animal in your world?
How are children educated in your world. Home school, apprenticeships, community day schools, boarding schools? Is school required, forced, punished?