Not so long ago, less than the span of a generation, a great heathen army was raised in the north. A force like none living had seen, gathered by the promise of loot and glory to last until the end of the world. They set sail, set their many gods against one, and they were destroyed without ever setting foot on shore.
The humiliation resounded through their culture. Raiders became traders. Gilded swords were melted down for coinage, ships were gutted to fit more goods in their holds. What once was taken violently would now be won cunningly, or else another defeat would end them.
The seat of their power, the city called Thaw, opened its doors for business. Attractions were built, halls in imitation of their warrior-heaven on earth where mead flowed in waterfalls, saunas and bathhouses altered to southern tastes. Money came in, fortune raised some and tossed down others, resentment and contempt spread like a fresh bruise beneath the friendly shopfronts. Disgraced killers turn to poison and magics before thought unmanly, gods that forsook their charges in their time of need are called on with whips and curses in place of offerings.
Change came to Thaw, and change comes again, tasting like death all the while.
Frost Giants: Steadfast allies of the northmen since time immemorial, whose ships of leviathan-bone went to their doom with the great heathen army. The giants took the defeat even harder. To them, it's the start of the world's dusk, a terrible and terminal cosmic decline. The majority retreated to glacial fastnesses in the uttermost reaches, there to remain in preparation for their role in the final battle, or sleep away in sea-caves to dream and sing with the whales. A few lost faith, lost themselves in drinking, gambling, whoring, and a few had their faith hardened, their blood and their hatred turned to ice. These latter giants seek new allies, once old enemies: the Sun-Eater Wolf, the Stitch-Lipped Liar, the Serpent Who Strangles Mountains, the Calming Lightning.
Locathah: Cold-blooded and glassy-eyed people of the seas around Thaw, long considered by the northmen to be their natural thralls. In the wake of the great heathen army's destruction, Thaw began to fear uprising by the locathah, as they lost much of the strength needed to keep the fish-folk in line. To preempt violent rebellion the locathah were decreed universally free, at least in theory, though in practice prejudice and disenfranchisement has caused them to remain third-class citizens, below even human and giant thralls, subsisting in the desperate margins of an otherwise increasingly prosperous society. Like the northmen the locathah too have slipped from many of their old ways and their old gods. These things have come to be understood as subservient to their new god, their liberator, who succeeded when all miracles before had failed
Valkyries: Thaw's heroes have died, and by turning away from the warrior's path Thaw has ensured that never again will more rise to the standards of the valkyries. They're out of a job. The consensus among their kind has been that if they cannot collect heroes, they will themselves become heroes. Of Thaw's sailors the valkyries sail the furthest. Of its hunters they hunt the direst prey. Of its conspirators who whisper of cutting down the merchant-princes and scourging the seas once more, they push the hardest in making this a reality. Beside this drive, a shared dread unites them. Their master is silent, the bridges to his realm burned, perhaps both consumed by the fleet-melting fire that rained on the day that Thaw was broken.
Wendigos: The northmen may have softened, but the north itself remains as merciless as ever. People still go hungry, and the will to survive so often overpowers the taboo of eating one's own kin. Temptation festers, humanity withers away, and another wendigo screams with the wind. When they can be caught, they're put with others of their kind in the underground asylum called the Hungry Quarter, fed by the dumped offal of sacrifices and the few who still practice senicide. The wendigos of Thaw are not hated, nor pitied. All who've been truly hungry understand the choice they made, and all this far north have been truly hungry.
Salamanders: The city and the fields that feed it are kept unseasonably, inhabitably warm by an elaborate system of qanats and pipes, supplied by the hot springs of the nearby mountains. These hot springs in turn are fueled by the salamanders that swim in their depths. Their slithering young are the bane of many a bathhouse, and the adults play a key role in the folk magic tradition of the region. Take something you dearly love and burn it, they say, spread the ashes in the boiling waters, and the salamanders will come like fish to chum. They'll offer up some inhuman wisdom or treasure in return. It's whispered that the great heathen army itself was gathered by their prophecy.
Draugr: The drowned dead of the great heathen army don't rest peacefully on the ocean floor. They spit out silt, shake the crabs from their bones, and they wander. Some walk to the far shore they hoped to invade in life, a plague to seaside villages and monasteries. Many returned home. They're the unspoken danger of Thaw's harbour bay, a symbol to revanchists and an embarrassment to the merchant-princes. The draugr hold court among scuttled warships, snatch fishermen who don't keep to the old ways, drag foreign priests squealing beneath the waves, and watch old friends from beyond the edge of the lamp-light.
The OG: https://githyankidiaspora.wordpress.com/2009/06/10/make-your-own-new-crobuzon/
Anne's challenge and Crobuzon: https://diyanddragons.blogspot.com/2019/10/new-new-crobuzon-city-of-stones-and.html