Creepiest place in the game? The Upside-Down Sinners
To anyone who has been to Deadwind Pass, you may know of the city (Karazhan) which is where Medivh's Tower is (don't try jumping off his tower. You don't survive) and some blocked off instance gates. A bit past the tower, you'll find a church with a graveyard across from it, and in the graveyard there's a blocked off crypt.
Once you get past the gate, you'll enter an unfinished area. No monsters or anything inside. Just a bunch of rooms with names like "The Tomb of the Unrepentant" or "The Crypt of Criminals."
One lovely room is "The Upside-Down Sinners" and in my opinion, one of the creepiest places in the game.
The link I posted also has some screenshots of the place (and much better ones I might add) but yeah... I can't wait to see this place opened.