Two words:

Shalebridge Cradle!


I...still have the dreams.....

THIS!

The Shalebridge Cradle from Thief 3! I played the whole game about 7-8 times, I love it
Other games where modders can take ideas from: Call of Cthulhu, Amnesia: The Dark Descent
I would love to see a well-made Shalebridge Cradle(even the monsters, how they moved...), modders, gogogogogog! (ofc half a year from now)

Off topic, I just started playing with Nehrim, it's mindblowingly awesome.

I hope it is a castle. or a sunken ship.

Sort of related.
Also, there could be a mission surrounding cursed pirates (not taking hints from Pirates of the Carribean 1...okay yes I am), or a similar group of cursed people.
For the mission you have to break the curse and the undead skeletons/zombies/etc return to their mortal human forms and you save them.

For something to be scary first requirement is that it has to be dangerous, was more scared sneaking around as a thief in the palaces in Oblivion than in the Dunwich building in Fallout 3, played it at level 20 before I got Broken Steel so the ghouls was easy to kill, I sneaked so I usually saw them before they saw me.
In the castles I risked being arrested and had to make be very careful to avoid the guards and other npc as if I got caught trying to fight my way out would just give me a huge bounty.

Dangerous enemies are more important than a scary atmosphere even if it’s also important.
Then you searched for scraps in the steelyard in the pit was pretty scary as you had few weapons.
Best idea would probably be to capture the player so you had to escape without your equipment, yes it would be far easier for mages.

Maybe it could be a Dwemer ruin where they were using a special volcanic gas to power their machines. However it has leaked out everywhere You could hallicinate and see the dwemer ghosts endlessly working and hear a constant thumping sound of tools on metal. It would get louder and louder until you turn round and see a massive centurion sphere standing over you radiating with ghostly energy.

Shalebridge Cradle in Thief 3 was one of the most terrifying gaming experiences ever. I'll never forget turning the electrical power on which gave you an unmistakeable feeling of having just awakened the place.

A lot of the fear came from not finding enemies, or anything, out of the ordinary for such a long time after starting. By the time something actually happens, your imagination has already run amok and you're primed to pee your pants.

Not a great game, but that level alone was worth the box price and is a great example of how to scare the player to death.

lol?

Yes please no light in a dungeon at all and high pitch massacer screams or growling in the distance.

I hope the devs have been playing Cursed Mountain and the Fatal Frame games and been inspired to come up with more interesting ways of dealing with ghosts - some kind of exorcism ritual rather than always hitting them with magic or silver would be nice. Something that gives you an extra feeling of vulnerability and even helplessness.

http://www.youtube.com/watch?v=DvD3U7MKBXk

A wide range of ghost types with creepy animations like in http://www.youtube.com/watch?v=pmZKPMCuzVQ&feature=related would be ideal. And lets not forget poltergeists and objects thrown at you.

The Haunted Hotel in Vampire: Bloodlines was great but heavily scripted - only really scary in the first play through, sadly. Ah, Shalebridge Cradle - the memories. I always put the soundtrack from that into the Oblivion dungeon music folder. Really creepy music, darkness and the unexpected - all key ingredients.