Question: In a horror themed campaign with a Lovecraftian feeling, a big part of the game is a constant feeling of threat, but without any visual stimuli other than glimpses, or sounds vaguely heard of things seething in darkness, and with investigation a big part of the game, contrary to fighting.

Having read *Heroes of Horror*, I am searching for ideas on how to actually motivate players to assume the role of investigator rather than executioner, and how to instil the horror of the unknown, of something that threatens but is not substantial, that cannot be seen or heard, but is there, and has malevolent intent.

I am thinking of D&D 3.5 as a system, but I am interested in answers that cover any system (Call of Cthulhu is unfortunately out of the question), more as role-playing and storytelling techniques rather than mechanical ones.

Answer: 
The biggest ally in the bid to creep the players out is their own imagination. The biggest obstacle to that is your own. When running these types of campaigns, less is always more. It's just about finding out what 'less' should include.

1. Descriptions should hinge around one detail- the players' imaginations should do the rest. It's not about gore, nor about ultra-detailed descriptions, it's about triggering the players' mind to go overtime. Hint at the unknown rather than assaulting the player with it.
2. Engage all of the players' senses. In fact, engage other senses more than sight; reducing the applicability of sight to the description helps to engage the imagination, i.e the strange coppery smell, or the vision obscuring smoke that smells/tastes faintly of burning meat.
3. Building upon the details with small incremental revelations helps to lead the players' to where you want them to be. The realization that something is missing, or that something has been lost after an encounter with the unknown makes it that much more disturbing.
4. Repetition helps to inure the players to what you're doing- especially if that repetition is rhythmic or predictable. Even if not predictable, there is definitely a short shelf-life for when it will no longer be effective.
5. It is said that the best lies blend a kernel of the truth. It is also true that the best horror blends elements of the every day or of innocence. Take something that is safe and everyday/innocent and twist it for an effective factor of creepiness, i.e. the evil prophesy delivered in a child's singsong.

There are gimmicky techniques that can be blended with these to make them more effective, i.e. the soundtrack that comes on at an unexpected time, turning the lights down/off, sending notes to players in a way that others can see, but forbidding the player to talk about what's on the note... but these are just gimmicks and are not necessary to invoke that feeling of horror. Engaging the players' imagination is the key.
It's a horrifying feeling for PCs when they get to what they think is the end of the trail, the cause of all the distress and pain and suffering, the root of all evil, and then there's a small reveal that tells them they are just beginning to scratch the surface of something much more profound.

The demented, inbred freak held captive in a basement inside the old mansion can drive PCs insane, control them with its mind, and send its minions against them in waves. The triumph of finally overcoming this foul villain becomes something else entirely when its last words are, "Finally, I am released. Finally I am free of it. If only the rest were so fortunate!" The PCs now know this adventure, which taxed them mightily, is nothing but the prelude to a much bigger battle against a tremendously powerful enemy with resources beyond imagining.

After bashing their heads against the minions of this unseen force, the PCs will start to realize the only way they have even a sliver of hope of surviving is to stop attacking its limbs, its proxies, and start trying to find its heart and its head. Once they're in that mode, it's easier to start introducing more bits of paranoia, because they'll be trying to fit the pieces together. Pretty soon everything will start to look to them like it's part of a bigger pattern.