A group of weary travelers, lost and seeking shelter, stumble upon a small town huddled in the foothills beneath the shadow of a massive mountain. The village is empty. No people, no animals. Signs of struggle abound. Overturned carts, doors smashed in, pools of dried blood. All the signs point to some sort of massacre centered around the what appears to be a small jail the citizens were building into the side of one of the hills. At the back of the semi-completed structure is a gaping hole leading down into blackness, the rubble around strewed with strange markings. Suddenly something screams with hunger, something still lurking in the foothills surrounding the town. Something still hungry.
I’m a big Lovecraft fan. Can you tell?
Anyway, the basic idea is that the townfolk, while in the process of building a new jail, came across a sealed cave. Foolishly they have smashed through the seal stone and have unleashed something from inside. I leave what this is up to you. It has wiped out the town and is still lurking nearby. If possible, have the creature (or whatever) always be just out of sight. Stalk the players. Feed on their fears of what they can’t see. Have fun with it.