Sort of like Dark Sun, but weird.
The “Universe” is a natural Dyson Sphere. A hollow ball with a Star at the center. Due to this fact there is no such thing as night time. There isn’t a word for it.
But, the sun is dying. It’s notably dimmer and more yellow light than what it was in grandpa’s time. It’s hotter, drying out, getting darker, all of which mean plants are dying. It’s kill or starve, tribe vs tribe, cut throat lives.
There is no metal other than gold. Weapons and armor are all leather, bone, stone, or wood.
Lastly, anything that can be made weird, go for it. Trading caravans don’t cross deserts on camels. They use giant sand snails the size of elephants to pull wagons. Salt flats galore? Sailing on wheeled barges is normal-ish for crossing them.
Swords are rare. Spears are the weapon of normal people. Hoplites, mostly, but the armor is not bronze. It’s ivory collected from massive animals or sea life like clams the size of suitcases and fed a statue months ago that grew a shell around that statue. Now it form fits a man.
It’s an opportunity to wander around and get creative with cultures, tech, and invent new, fantastical weapons, animals, plants, and customs