The city of Caulderon is the mythic flying city. Once a magnificent city on a cliff, it was saved from being lost to the sea by being lifted by alchemical means. It was filled with impossibly tall shining spires standing above golden domes. The sunlight striking it is said to blind those who come to invade the city. The people lived in this magnificent city in health, wealth, and safety. They rode Griffons and created all sorts of creature. Caulderon was known for its magic, its alchemy. In the old tongue, the word Caulder means alchemey, from the word Cauldron. It is from their alchemey that their great wealth and comfort is derieved.
Legends (and Elven History) states that the floating city would visit The Lands once every few years, blown by the winds. They would trade for things and sell their magikal goods. After a year or so, their cities would be be blown to other places. It has been over four hundred years since any credible source has seen the floating cities. It is the thing of legends.
Then why has one been seen over the Land?
The PCs are hired by undead to rid their village community of an invasive necromancer.
As the PCs make their way, wherever they are going, they spot two zombies. The zombies approach but before the cleric can turn them, one starts throwing coins at the PCs while the other pleads with them, unable to pronounce the letters "L" and "H" due to some missing gums. "Peeth issen...no 'arm...coin...peeth issen!"
If the PCs don't slaughter the two zombies immediately, they will eventually come to learn that the two were chosen to find help by their brethren. The zombies want to hire the PCs to rid their community of an unwanted pest. An opportunistic necromancer.
Apparently, a small benign community of undead have taken residence in an abandoned village, living out their undeath as peacefully as the undead can. Recently, a malicious necromancer has invaded the village, and plans to enslave the entire populace with his malignant spells, raising a small army.
The PCs must battle the vile necromancer, even as he animates the very folks who hired the PCs in the first place, to slaughter them.