Halloween 2012 Day 5: The Descent (2005)

I enjoy the outdoors. I've been hiking a few times in the Tetons, canoed through South Jersey swamps, climbed around Rock Canyon in Utah, etc. The biggest draw with that stuff for me is the remoteness of it all. You're miles away from anyone else and disconnected from the physical and metaphorical ties that bind us to our modern concept of humanity. The Descent is a movie about that disconnect going wrong.
The Descent is one of the most suspenseful and absolutely terrifying experiences before the monsters are even introduced. Sara, having recently lost her husband and daughter in a car crash, is taken spelunking with some of her friends, all experienced-but-casual outdoorswomen. They dive into an unexplored cave system and quickly find themselves in way over their heads against an opponent as fearsome as mother nature. When events head from bad to worse, they discover the cave system isn't as unexplored as they assumed.
The limited lighting and sheer darkness of this film puts across this incredible sense of claustrophobia and the acting and direction are absolutely top notch. It relies fairly heavily on jump scares as the film progresses, so if that puts you off, you might want to avoid it, but they managed to terrify me. The plot is whisper-thin but the atmosphere is so strong it doesn't really matter. The Descent is a scary, violent romp right into the dangers that the dark hide.

EDIT: I'm told that there is another cut of the film that removes a lot of the nuance and character of the film and rewrites the ending to something insipid, so please, by all means, avoid the US Unrated cut of The Descent.