A community of lets say 50 vampires, living in a village covered from the sun in a valley (not a cave).
Why not a cave? Because they want to be normal, like normal people. Therefor, they also do not drink the blood of humans, but only boars, bears, rabbits & other creatures.
Only way to find / get accepted in this village is to become a vampire yourself.
This way it can also create a gate to more difficult tasks (since your no weak player anymore)
You could have a major quest around it to extermine the struggle of leadership.
Be the leader yourself, or let one of two other potential leaders take the crown.
Change the vampires to do what you want them to do. Create war, or remain pacifists.
Help them in their poisoned lifes, or whipe them out as a vampirehunter (you could get that quest in a nearby town and take a follower with you)
There is a lot of potential in this idea, i think.
So what do you think? Vampire city or no?