I got this idea a while back, but I haven't been able to implement it.
One of the PC's is a cop from the local town, who got called out to the middle of nowhere in a forest, supposedly where a very small village or town is supposed to be. Obviously, there's a lot of fog and what not. The PC goes with at least 12 men from the force, because they heard some deep shit was going down.
This is where it starts. The PC and the boys drive up to the only way into this town, which is a single rope bridge stretching across a small canyon. The rope bridge is cut, and the fog is thick enough so that they can't even see the other side at all. As the PC discusses ways to get across with the boys, a voice comes from the other side of the canyon.
"Hey, is somebody there?"
". . .What? Who's over there? Who are you?"
"Oh boy, am I glad that you guys are here! Listen, something strange is going on in this town! There are these. . things. . .Listen, can you guys get me across? I really just want to go ho-"
The voice is cut off, and after a few moments of silence, a loud splash is heard from the bottom of the canyon. If the PC investigates, all he finds is a torn jacket, looks like someone was impaled.
Then, the PC will probably enter the town, for whatever reason, then the rest of the adventure happens, maybe the PC meets the other players, etc etc. However, by the end of the adventure, everyone except for the first PC will have died, and the first PC will get the feeling that if he doesn't flee soon, he'll die himself.
He makes his way back to the bridge, only to discover that once again, the rope bridge has been cut down. As he stares at the bridge, crest-fallen, he hears voices coming through the fog from the other side of the canyon. He naturally calls out to them. When they answer back, the PC feels relieved and calls back to them:
"Oh boy, am I glad that you guys are here. . ."