The City Standing Like a Candle in the Night - a walled fortress inhabited by a great and advanced civilizations able to magically last the night. The PCs would begin there, at the very bottom rung of the social order, early in the night - just a year or two in. Surrounding them would be all kinds of opportunities for adventure. Intrigue in the City itself. Raiding nearby "digger-type" settlements with huge underground caches of valuables (perhaps one of which is abandoned and forms, essentially, a megadungeon, with many of the defences still intact). Stealing from dwarf or gnome toll-takers at a nearby migratory choke-point. Searching for caches left by migratory peoples. Tangling with orcs and other night creatures. Searching for hermits or elder beings who do not move with the regular cycles? Trying to track an infamous Laputa-like floating castle?
As a setting, I think rather than being early in the night I would place the City at the precise point at which dusk segues into night. This is a world in which the sky is dark grey clouds laced with the orange-gold of a permanent sunset. It is cold but not glacial. Snow lies in patches but when the weather comes it is mostly sleet or hail. The forests and mountains are quiet: the animal life is preparing for hibernation or migrating to follow the sun. The last stragglers of the nomadic tribes pass to the West. The creatures of the night begin to appear. The things which have spent the last century underground begin to stir...
In the vicinity for PCs to explore/interact with are:
- Underground stores left behind by migrating nomads
- Lairs of hibernating beasts
- Magic moving castle of an archmage which prowls the world searching for magical artifacts
- Cults or religious orders who worship the night (or perhaps view it as the coming apocalypse/millennium)
- Things emerging from the night itself - demons, wraiths, ghosts and so on
- Dwarf settlements permanently underground, some of which lie abandoned
- Mysteriously-abandoned "digger-type" citadel
- Vast reindeer herds who move with the dusk gradually eastwards, and their herders
- Settlement at a specific choke-point for travelers, run by psionic gnomes
- Things within the City itself (natch)
- Hermit arch-mages, witches and so forth hunkering down for the night
- Elder gods who stalk the night