Whether it's a brief mention of the kind of food dragonborn cuisine would consist of, or an offhand comment about how a Beholder would wear glasses, what was a small, almost silly detail that cemented the idea of your world further? 

My tavern proprietor is Deaf. 

She is also one of the first NPCs the party interacted with as the campaign started. It provided a fun moment for the players to feel like they really were strangers in this small factory town, because the locals at the bar were snickering at the party's inability to get her attention. It also provided the players with a challenge, since they needed to get info from her and none of them know her sign language.

On my side of the screen, having her be Deaf makes my world feel...more real, somehow. It's a little facet in this lifelike jewel of a story world: a woman owns a popular bar, and all her neighbors have learned to communicate with her because they like her beer. That's just life in sleepy Silverlake - complete with the sport of watching outsiders make utter fools of themselves when trying to order said beer when the owner's back is turned. :-)

My game has four regions that are influenced by the elemental planes. There's a particular kind of grape in the region influenced by the elemental plane of air that can't grow in the other regions. It adapted to being grown under constantly windy conditions; in still air, the grapes get too heavy on the vine and fall off before they're ready for harvest. The wine from these grapes is highly coveted all over because it can't be grown anywhere else. 

The city my players are in (and across the rest of the region) is matriarchal. Currently, and very old lady rules the city (she's about 70,), while her son helps out. Her daughter (who is older than the son) has gone to study, and when she comes back will rule straight away. Even if she were younger, it would say the same. 

The halfling race is an incredibly military strong race, similar to dwarves

 There are two moons in a world my friend and I made. One is called Silas, and it is humongous and quite dim in the sky (think of the sky in the movie Avatar - the one about the blue aliens). The second one is called Janza, and it is a bit smaller than our moon and blindingly bright. Janza also eclipses the sun every month, as the orbits of the sun and Janza are in line, rather than eccentric.

In towns and cities with a wall, you must obtain a license to carry weapons in order to carry more than a dagger for a commoner or a dagger and rapier for a noble.  This is intended to reduce murder hobo tendencies.  

My old homebrew world had a massive open-air marketplace that was changing every day due to traders coming and going. There were taverns all around the edges, where people could hire "runners" - those who knew their way around the market - to find the items they were searching for; going into this marketplace without knowing where to go would inevitably get you lost (but could still provide some interesting finds!)

The elemental planes in my campaign have different unique smells. Like, you smell normally, but also there’s one pervading scent that covers everything revolving around that plane. Fire is the scent of burning sulfur, water is salt, earth is, well, dirt, and air is perfume like.

The tradition of blood candles on the coast.  For a small sum a candle can be purchased that will burn until the lifeblood of the person offering the blood expires.  Very popular in sailing communities and some miners inland.  

The fancier vintners near Evereska have levitating platforms to grow the best grapes near waterfalls.  They invest heavily in the Academy there and provide a lot of internships to try and capture the best enchanters graduating there.  Many rings of levitation are used by the workers in the vineyard in some locales... and because the work is relaxing, many of the elves in Evereska undertake a season of work in such environments.  Few are full time employees as such, so it provides a challenging landscape for the owners.  

Currently I'm working on a racing league campaign and there is going to be a lot of new things invented for that I can already tell.  But creating new magic devices or solutions is the fun of a high magic style world.  

Quote from Grayfax >>

The tradition of blood candles on the coast.  For a small sum a candle can be purchased that will burn until the lifeblood of the person offering the blood expires.  Very popular in sailing communities and some miners inland.  

The fancier vintners near Evereska have levitating platforms to grow the best grapes near waterfalls.  They invest heavily in the Academy there and provide a lot of internships to try and capture the best enchanters graduating there.  Many rings of levitation are used by the workers in the vineyard in some locales... and because the work is relaxing, many of the elves in Evereska undertake a season of work in such environments.  Few are full time employees as such, so it provides a challenging landscape for the owners.  

Currently I'm working on a racing league campaign and there is going to be a lot of new things invented for that I can already tell.  But creating new magic devices or solutions is the fun of a high magic style world.  

 Man, your ideas sound amazing. Love them. 

Aw... thanks... I'm just out here having fun.  I'm trying to come up with a good system of combining scrying spells with a display pane of a wall.  Not quite television, but very good for rich clients to have views of other parts of the world.  Originally I was thinking this would be for viewing mountains or scenic overlook types of things... but with the idea of the racing league, being able to create a permanent scry device (portable) that is viewable from a magical wall would allow for fans to view some of the more epic racing mounts and moments available to the D&D world.  Cause flying isn't going to be able to be attended well by the betting populace with deep pockets.  And as the "tracks" will change for the premier league, the fans can be in a fancy city (think Dalaran) and view the races every day.  Kind of a Clipsys System (Roger Zelazny's Alien Speedway) meets Dinosaur Racing in Chult with Team Sponsors (and somehow a hint of Scooby Doo).  Of course with Message and Sending stones, the results could be broadcast all over the world quickly.  And very possibly a whole Arcane team for providing information scattered throughout the land.  The vision is coming clearer but there is a lot of room for details to bloom and grow.  And that's just one aspect... the magical environment surrounding the better circuits would need to be there.  The foods needed for the mounts.  The mounts themselves and how to house them.  Portals to and from event areas.  Obstacles (natural and spell crafted).  Magical souvenir items (don't want to quite get to Harry Potter level of living photos / portraits, etc.).  

Oh... never mind Sending stones... we need boards that when written on are copied to other boards of the same kind scattered throughout the world.  Race updates in near realtime via magic!  Another good use for a levitating magician, but where penmanship matters!

Quote from Grayfax >>

The tradition of blood candles on the coast.  For a small sum a candle can be purchased that will burn until the lifeblood of the person offering the blood expires.  Very popular in sailing communities and some miners inland.   

One element I really appreciate in worldbuilding is the existence of magic items that make perfect sense in a world of magic but would be relatively meaningless to adventurers (and thus unlikely to show up in game materials.) 

While it's not so "Small," I find it cool. 

Both me and my friend have homebrew worlds of our own. My world wasn't made by any god, but by sheer magical force. Originally, it was created as a space in a void, where used arcane energy from other worlds would be collected and sent back into the multiverse. However, in my friend's world, there was an event that released a massive amount of this magical energy. All of this energy running back into this collection point at once created a whole new world. I just thought it was nice that our settings could be connected like this.

I have created several constellations, including the myth behind each one. My favourite is Casteron - five stars in the shape of an anchor, which always points due north. It is said that Casteron was an ancient sailor in the days when wicked Umberlee would deceive and mislead ships in order to make them sink. Casteron threw his own anchor into the sky and climbed the chain to live among the stars. Every night he places the anchor as a beacon to guide other ships, and every morning he hides it while Umberlee seeks to steal it.

Also, short beards among dwarves are a sign of low status since the working class must often trim them for safety; thus the nobles of a particular city consider it scandalous that their lord keeps his rather short, but the rest of his people find it makes him seem relatable. There is considerable talk about the rumor that the king might name this lord his heir, and what it would mean to see a short-bearded dwarf on the throne.

The first session of my campaign sent the characters after the crown of an long-dead hero called Orvain Kobold-Slayer. Since then, I've name-dropped Orvain, along with a few other heroes, here and there throughout the game. Since my world is deeply based on folktales and Arthurian legends, it's cool to hint that the it has its own past stories.

 The small-ish town of Faxxe had, prior to the troubles, survived on the trade route going through their area and exporting bricks. After the troubles began and the trade caravans stopped coming, the town decided to continue their production of bricks and just convert the wooden buildings in the town into brick houses. Then at least there was something to do.