I thought it might be fun to see how other people would run with different plot hooks. I will try to keep the scenario as neutral as possible so allow as wide a range if settings/systems as possible.

Inspired by traveling on expressways in mountainous regions of Japan and the train to Machu Picchu. Sometimes as your vehicle crosses a bridge you look out the window of your car or train carriage and see a small village in a valley, but from your limited vantage point you can’t see how the village connects to the rest of the world.

Setting requirements. Some form of transport infrastructure through mountainous regions. Examples include expressways, canals and railways.
System requirement. Probably requires a system where flight is non-trivial.

Set up.
Because of [plot reasons] the party is exploring/traveling in a mountainous region. From a high bridge/viaduct/aquaduct they see a small village nestled in the valley below. From a cursory look everything appears normal. The ethnicity is normal the architecture is normal, the farming is normal, there is no outward appearance if anything unusual.

But there are some peculiarities.
1. The village does not appear on any map. People have different names for the village, all of which are a variation of “that village in the valley”.
2. You can find no one who has actually been in the village or knows how to get into it.The people from the North side think the access is from the South, and people from the South think the access is from the North. Other people may suggest that the village is accessed by the river. No local is curious about the village, it’s just always been there.
3. The village is essentially located in a box canyon with no known exit or entry points.
4. The bridge you can see the village from is a single arch bridge that is unusually, but not impossibly long. Bridges of similar length are considered marvels of engineering, but this bridge is not remarked upon anywhere. Research into the bridge will reveal that there are no records of the construction of the bridge. You can find records of the roads leading to the bridge, but no records of who built, paid for or designed the bridge. Physical examination of the bridge will show it fits seamlessly with the local roads/bridge technology and is completely normal apart from the unusual length.
5. Organizations that you may expect to have a presence, such as religious groups, traveling bards the post office do not have a record of who is responsible for the village. The people from Town A, assume it’s Town B’s responsibility and vice versa.
6. Scrying on the village or spying from a distance will show [something odd]. Examples might be the crops being 2 or 3 weeks out of sync with other crops in the area, something unusual about hair color, unusual patterns of activity,

So what’s in the village?

Please include the system, setting and party level (if appropriate). Also whether this fits into the main plot or is a side quest and why the party would want to investigate this otherwise normal seeming nondescript village.
Feel free to add any other details/clues you think may be relevant for your take, eg travelers mysteriously vanishing or more travelers than you’d expect for the region, climate peculiarities such as mists or unusual heat, an increase or decrease in expected monsters/dangerous animals.

I have my own answers, which I will post later, but I want to see what other people will do with the set up.