The thaumaturgic forces unleashed by the Great War have left much of Ealderde strange. For an example of just how weird this transformation can be, one need look no farther than Lumière,the former capital of Neustrie and the Gallian Alliance. Once Lumière’s lights were emblematic of a city that never slept, a place of art and culture. Today, Lumière is a bombed out ruin, and the amber luminescence that crawls or flows through its streets and buildings is something of another world.
The thing is alive; almost everyone agrees on that, but little they agree on little else. Is it matter? Some gelatinous substance similar to the strange denizens of the underground? Or is it pure energy, somehow thickened and held? If it’s the latter, it’s light with no heat.
In the day, it seems to hide in the skeletons of buildings, perhaps fearing the sun. At night it pours forth and spreads out over whole blocks. Rats and vermin flee it. Living things it touches develop strange tumors or growths. When it first rose, victims caught in its path were left rooted to the spot, transformed into masses of cancer.
The glowing touch of the thing seems to have created at least one mutant species. The wild swine that moved into the city to root and scavenge after the devastation of the war have been changed. They've grown large, and bloated and pale as grubs, with eyes that glow with a paler yellow that the thing. Though they can’t speak, they seem to have evolved an evil intelligence. They roam the streets in herds, seeming to take pleasure in spoiling what remains of the works of man, and looking (though they're hardly picky eaters) for their primary form of sustenance: fungal spores.
The Mushrooms, the swines' unrelenting foes, resent their progency being consumed by the swine with a displeasure that's more cold practicality than horror. These fungal sapients likely lived beneath the city even in previous times (certain legends hint at their presence) but when the humans fled they saw an opportunity. From their inhuman alchemical laboratories they create structures from fungal stock and weaponize molds to strike at the swine and keep humans away.
Looters and treasure seekers make forays into the ruin of Lumière, but it's a dangerous undertaking. Even if the poured-honey creeping of the luminescent thing can be avoided, there are the packs of hungry swine to be outwitted, and the silent and dispassionate Mushroom scientists to be dealt with.