Human beings have a primal, unshakable fear of the unknown. It's something that's been hard-coded into us by evolution: back when we were all living in the treetops, the dark places of the world held a whole host of predators ready to tear us limb from limb; the deep night was one of the most dangerous times of day. The most skilled, masterful horror artists use this fear to great effect: the human imagination is, after all, an incredibly powerful tool.
In other words, the less you see of something, the more frightening it is.
What you'll be seeing.
That's the whole basis of the virtual reality game "Deep Sea" - though referring to it as a game somewhat cheapens the whole experience. It's a rather masterful, innovative use of technology, and proof that the tech necessary for truly immersive virtual reality already exists. Deep Sea is an audio-only title where players don a diving helmet equipped with electronics which completely shuts them out from the world around them. They then take up an electronic "harpoon gun" which will serve as their weapon. This array features a number of directional sensor in order to determine which way the player is facing.
That's when the real terror begins.
There is no visual element to Deep Sea. The player is subjected to an orchestra of alien sounds, which they must use to judge the location of the creature which is stalking them. This requres an immense amount of focus - enough that the player must actually regulate their own breathing. Once the player thinks they've locked down the location of the creature, they fire the weapon, desperately hoping they'll hear the beast cry out in pain.
A close approximation of what you'll imagine.
Likelier than not, they'll just hear the shot vanish into the void of the deep ocean. Death seems an inevitability: a terrible, inhuman roar coupled with the screams of the player character's gruesome death. The game is played in public, with the site emphasizing how this "reinforces the sense of being surrounded by invisible danger."
Sounds absolutely terrifying. I want to play it. You can find the game here.