The Descent (2005) written and directed by Neil Marshall
A group of girlfriends get together and go on an extreme adventure once a year. One of the group, Sarah, had a horrible car accident on the last trip. She was okay but her husband and her daughter died. So she really isn't okay, she's having nightmares that sometimes seem like reality. She meets up with the girls again anyway and they explore a cave in Appalachia. The only problem is as they go along there's a cave-in and they are in a different cave than they originally planned on spelunking. They are lost in an unexplored cave with no hope of help coming to find them. If that wasn't bad enough, the cave is not uninhabited and soon they are fleeing from or fighting with some underground humanoids who are very hungry.
The movie has a lot of atmosphere once it gets into the caves. The story, with the claustrophobic climbing through rock tunnels barely big enough to fit them, is scary even before the monsters show up. Tensions among the group become very high and their friendship is tested and even broken some times. The monsters are horrifying to look at though they mostly appear in quick flashes, even during the fight scenes. The fights have a lot of editing, making them more tense to watch but not turning them incoherent.
If you want to see a really scary movie, this delivers the goods. Also, there's a lot of nice visual references to other films like The Shining, The Evil Dead, etc. Film buffs get a little reward too!
Parental Advisory: The gore level is pretty high. Plus there's some recreational alcohol and drug abuse along with the typical foul language in an R-rated film. Also, the link below is to an "unrated original cut" of the film, so I don't know what they've added/taken away.