This is very loosely based on a nightmare my wife had the other night. In the spirit of Halloween, I thought it might make for a nice, spooky RPG location. I had the default Lamentation of the Flame Princess setting of 1600s Europe in mind while writing this, but you could fit Avarton or some place like it into all kinds of games.
Avarton is a large village (or small town, depending on who you ask) of about 500 people. The town is fairly prosperous for its size because of its large gristmill, which serves the surrounding communities, as well as its lead mine, which shows no signs of running out any time soon (unlike other mines in the area). The town is noted for having very beautiful foliage in the autumn, and for growing great big pumpkins and surprisingly tall corn and wheat.
Most outsiders don't spend more than a few hours in the town at a time, and almost no one stays overnight unless they live there. If asked about it, most people probably will not have given this trend much thought, but some likely explanations may be offered. The simplest reason is that there are other communities nearby, so people who don't live too far away just go home to their own beds at night, while strangers to the area tend to choose much nicer accommodations elsewhere, rather than the single plain-looking inn (and largest tavern) in Avarton, the Grubby Goose.
Some might point to another problem: People who spend more than a day in Avarton tend to experience strange tingling sensations and numbness, abdominal pain and nausea, muscle weakness and coordination problems, and some mild confusion. This illness goes away after about a week spent in town (or a few hours if one leaves town as soon as the problems start), as suddenly as it comes on, which is why the residents don't seem to suffer these symptoms - they all just "got over it." Still, this mysterious and temporary sickness is unpleasant and inconvenient, so outsiders who know about it just don't stay in Avarton long enough at a time for it to manifest.
For every 24 hours they spend in Avarton, PCs must make a saving throw vs. poison or else come down with this sickness. Once contracted, the sickness lasts for 1d6 days in town or 1d4 hours outside of town. The sickness can only be caught by a PC once per stay in Avarton. If a PC leaves Avarton for more than 24 hours, they are at once again risk of getting the sickness. A sick PC suffers a -1 penalty to all attack rolls, saving throws, and skill/ability checks of any kind.
(Oddly, none of the residents ever seem to experience any signs of lead poisoning, not even the miners. Unless you count the brief illness they all "got over" upon first moving to the town, that is, and even that doesn't seem to apply to people born in Avarton.)
The final reason outsiders don't stick around is a bit harder to get people to admit. When the sun starts to go down in Avarton, many outsiders feel a strong sense of paranoia. The feeling is usually described as a certainty that the people around you want to take away something that belongs to you, or that you've accidentally taken something that belongs to them and they're plotting to take it back.
At sundown, any PCs in Avarton must make a saving throw vs. magic. Success means they experience this paranoia, which may serve as a warning sign. Failure means they feel nothing unusual.
Residents of Avarton suffer a collective magical delusion, or rather a pattern of delusions. Between sunset and sunrise, the people of Avarton tend to believe that various objects which do not belong to them are in fact their rightful property, and always have been. If you set something down on a table and move away from it, within moments someone will come up and blatantly try to take it, because they will genuinely think it belongs to them. If confronted or questioned about this, not only will the "thief" be confused and insulted by your objections, but any other villagers nearby will also back up their claims of ownership, making up stories of seeing the "thief" buy or make the object or receive it as a gift, seeing them carry it around or use it on multiple occasions, seeing it in their home, etc. They will genuinely believe these stories, not realizing that they are lying. The "thief" will absolutely refuse to give up their "rightful property," and if it comes down to it, every single other resident of the town will side with the "thief."
And in all likelihood, this will happen over and over. If you set something down and walk away from it, it will be gone when you come back. Those horses you hitched up out front? Farmer Bill is taking them home right now. The trail of breadcrumbs you left behind you in the wheat maze? Little Sarah has been following behind, picking them back up and wondering why she left her collection of favorite breadcrumbs out here. Did you set your mug of ale aside to go take a whiz? I hope you didn't plan on drinking that.
All it takes for one of your possessions to be potentially "up for grabs" is for it to not be in physical contact with either your body or an item you are wearing (like clothing, armor, or a backpack) for about 20 seconds or so. However, just because it's potentially "up for grabs" doesn't mean a villager will necessarily lay claim to it right away. If you let the item out of your line of sight, it will be stolen almost immediately if possible, but if you stay nearby the curse could take a while to present a "thief." In such cases, there is a 1 in 6 chance that any such item suddenly "belongs" to a villager every 10 minutes. Separate rolls should be made for multiple items.
When a villager lays claim to something between sundown and sunup, they will not let the matter go. They will get the law involved if you push the matter, and if that doesn't get them what they want, they will gladly whip up an angry mob. And while new delusions of ownership cannot be formed during the day, old ones from the nighttime will persist permanently, so don't expect Farmer Bill to come to his senses about those horses just because the sun is shining. Even if they don't need the item, or wouldn't even ordinarily want it, they will refuse to give it up under any circumstances. Perhaps the people of Avarton would have been a bit more laid back about the whole thing a few years ago when the curse first started, but you can only see other people walking around with your stuff so many nights in a row before you start to get a bit defensive, you know?
When a villager steals from another villager in this way, everyone will agree that the stolen item does indeed belong to the person who took it; even the person who was robbed will agree, though perhaps not right away. Villagers accidentally exchange items like this every night and usually think nothing of it (outside of the occasional, brief argument about why Person A had taken things from Person B), since their delusions essentially create new memories of ownership. If the PCs pay attention, they may notice this strange activity happening around them before they have a chance to fall victim to it themselves.
The Grubby Goose
Tied up in the basement is a merchant who tried to peddle some wares after sundown and got extremely hostile when everyone just started taking his stuff without paying for it. He caused a scene, everyone involved overreacted, violence broke out, and just like that he ended up imprisoned and badly beaten. He had all kinds of deeds and other legal documents on his person, which now "belong" to the enraged townspeople. Said townspeople have been torturing him for the locations of "their" property and money (as granted by the documents they "own"), and for the merchant's signature wherever it is needed to make their ownership "official." The merchant is stubborn, so he may hold out a while before he finally either gives up everything or dies. His family would pay generously for his safe return. Not everyone in the village knows about the kidnapped merchant, but enough of them do.
One of the mill workers has been possessed by a vengeful ghost. She has taken to putting small amounts of lead in the flour. This doesn't seem to affect the people of Avarton, but the citizens of nearby communities are slowly starting to feel the effects of this contamination. The mill worker has also set up a strange shrine in a hidden room beneath the mill. On top of an ancient stone altar stands an upside down cross woven from corn husks. A lead knife and a bowl of wheat husks, both caked with dried blood, also rest on the altar. A summoning circle has been made from flour and surrounded by five pedestals topped with bowls of grain and pumpkin seeds. Trapped within the circle is what looks like a living lead statue of a gargoyle-like creature with a jack o' lantern for a head. This creature introduces himself as Stingy Jack, a representative of the First National Bank of Mamona. "Would you please be so kind as to fetch me my ledger? I dropped it somewhere in the mines, clumsy me! I'll make it worth your while."
Every major holiday, the people of Avarton hold a feast at the big stone pavilion on the edge of town. The parties here can sometimes last from noon to midnight. One small stone above the pavilion's fireplace is carved with an upside-down pentagram. If asked, none of the villagers seem to know why it's there. If the stone is removed, a hidden compartment is revealed. It contains a key marked with the same pentagram and a map indicating a certain tomb in the town's graveyard, with the words "The wages of greed is life," scrawled beside it.
The Corn Maze
Every fall, the people of Avarton celebrate All Hallow's Eve with an odd tradition. They cut a maze in one of their largest corn fields and hide jack o' lanterns (made from truly huge pumpkins) in all the dead ends. These jack o' lanterns contain not only candles, but also coins and other treasures, "given" as playful offerings to the ghosts and ghouls of the season. Of course, this treasure always ends up taken by somebody eventually, but not until after the holiday is over - unless some outsiders decide to take it first. Taking shortcuts through the maze is ill advised: not only is the ground pitted with holes just the right size for twisting your ankle, but the "walls" of the maze tend to be filled with booby traps left by the villagers. It's part of the tradition. Besides, the maze is there for the spirits and monsters, so you have no business trespassing. Also, there's always the possibility that the maze is genuinely haunted. Hey, did that scarecrow just look at me funny?
The Lead Mine
The deepest level of the mine connects to an ancient temple, sealed and buried for ages. The miners breached several walls of this chthonic complex years ago, but have not disturbed it since, except to make the yearly offerings necessary to ensure the mine does not run out of fresh lead to sell. The structure bears features of Babylonian architecture, along with styles of construction and artistic flourishes which are harder to identify as being carved by human hands or invented by mortal minds.
(Alternatively, you could put the Temple of Greed here or something.)
I imagine Avarton would need to be fleshed out a bit more to make it ready to run - you'd need NPCs, maps, encounters, etc. If I ever run or revisit this, I'll have to let you folks know. In the meantime, I hope this can serve as inspiration for somebody. Happy Halloween!