the Campaign setting i was going to run (Expedition to Castle Ravenloft) Its a story more or less tied into Bram Stoker's "Dracula" (in terms of setting, but not plot).
The party of heroes enters Barovia, a Land choked with the essence of undeath and fear. The vast forests that wall the country are veiled by a foul mist, and whispers and laughing can are heard form the fog on a regular basis. Upon investigating this land, the heroes discover a foul plot to murder all of Barovia's citizens and unleash them as an undead horde.
Barovia's castle Ravenloft has been empty for years, for the count of this house died many moons ago.
But a light has recently been seen in the tallest of the castle's tower, and a chilled wind blows from the cliffs and crags from which the looming citadel sits. There, Count Von Strahd awaits.
I'd probably run a QUICK 1-time session, start you all at level 10 and then skip all the sections about exploring the country, forests, ruins, churches, graveyards, crypts, dungeons, catacombs, bandit camps, ghoul raiding bases, or survival-horror like encounters with a villages overrun with zombies (though this is hilariously fun, imo) Players would start at the drawbridge of the castle, and we'd pretty much "Castlevania" it up until you get to the boss, haha.
like a WoW instance or something.