Not much feedback on the previous but lets get it out of my head once again :)
It would be an event location, somewhere in the wilds (there would be gossip in the nearest tavern how to get there if you are lucky). It would be represented by major settlement with Dark stone keep towering above it. New art for the settlement would be needed (The houses would look in bad shape, there would be only scarce resources across all shops, there would be temple art but abandoned, there would be few recruits with worst backgrounds (cripple, beggar etc.)) once you enter it, it would be just a normal city interaction with nothing much of interest.
If you are near the city at night or enter the city at night there would be high chance of ambush from vampire ghouls (mindless, drained humans, fast with claw attack, on hit heal HP) depending on how the devs want to put the difficulty, I would see it as numerous attack, not an early game fight.
On your return to the nearest human settlement there would be mission from the House to the location with 3 skulls.
The local noble would require your aid in investigation of what happened to his brother who has his keep near by. He sent envoys, but nobody returned and the rumors he heard are keeping him from going there him self. There should be a hefty sum on that contract.
As you return to the keep, event flavor text will come up with depiction how you are approaching the keep as you near it everything seems to feel more of death. As you arrive to the doors you would have two options: knock on the door and run away. Run Away will cancel the event until you return again. Knocking on the doors, would result in the doors opening just as you were about to knock on it, huge doors opening as by themselves.
Inside would be only dimly lighted with candled here and there, party would enter and they would meet the keep owner, pale individual in full plate armor. We would invite you as dearest guests to have some rest and spend a night in the keep to keep him company as he haven’t had guests in years.
You either accept the invitation which would result in random members being feasted by the Keep vampires, giving HP malus for the oncoming fight and starting exhausted at the beginning of the fight. Or you can reject the hospitality by which you start the fight immediately. I don’t think there are any indoor fights so far so lets say as you reject the offer the vampire Says “So Be It!” and the keep goes pitch black your party then barely rushes out of the keep on the village square outside.
Keep owner in full plate, able to teleport like Necrosavants, could have some nasty two hander, heal by HP dmg. He would either have a court represented by additional vampires with various gear that would again teleport, heal by HP dmg. Which you would need to take care of.
Or the keep owner could be the only fully developed Vampire and he would have a flock of vampire ghouls that would rush at you. In this case he could have also an ability to spawn (masters calling) additional ghouls that would spawn on edges of the map (as they are very fast they would be at the party right away) this would need to be set as per difficulty expectations.
Once you kill the Keep Owner all the ghouls will die instantly.
Legendary Drop: Possibly either plate armor that would heal you or two hander that would heal on HP dmg.
Once complete you would return to the noble that requested your help you would give him a signet ring of his brother that it was necessary to stop him. He would grant you the cash and the settlement you freed would be added to the house you did the work for. As the settlement would be in the wilds there would be then more difficult contract to be found there as a reflection of dangers that want to now take the keep for themselves once the original owner is no more.