Forget Silent Hill or Fatal Frame. You know a game that's terrifying? Bay12's Slaves to Armok: God of Blood: Dwarf Fortress II, colloquially shortened to simply Dwarf Fortress. If being one of Armok's slaves wasn't bad enough (it isn't), consider that the game's visuals are totally in ASCII, that there's no user interface to speak of, and that all of commands are mapped to the keyboard.
In case you're not hip to frustratingly opaque indie games, Dwarf Fortress is a mix of city-building "God game," real-time strategy, and roguelike, all wrapped up in a procedurally generated bow. Wonderful things can happen as you build your eponymous Dwarf fortress (it can be flooded by lava, for example), but trying to figure out how it works is like trying to dig a hole to China with toothpicks. That've been jammed into your eyes.
Luckily, developers Jonask and Solifuge have addressed at least one of the barriers to entry into Dwarf Fortress: enter Stonesense, an isometric visualizer that runs alongside the game, ostensibly providing the player with some visual orientation that's easier to handle than the original ASCII. The open-source project is currently in alpha (whatever that means), and the DF community has been contributing sprites.
You can download the file here (.zip), and check out a video of Stonesense in action in the video embedded above.
Maybe I've been spoiled by modern standards for aesthetics, but the impenetrable graphics surely aren't helping Dwarf Fortress win the hearts and minds of any but the most dedicated gamer. Stonesense makes another attempt at Dwarf Fortress tempting, but I'm still not sure that, even with the facelift, I'll ever be able to wrap my brain around the deep calculus at work here: that sounds like a fool's errand to me.