As a horror fanatic, this film floats at the top of my list of best scary films in recent years. The setup feels like it moves quickly and seamlessly into the main storyline, but that's because it's so beautifully shot, well-acted, and scripted so that we know and care enough about the characters to worry once they belay down into the dark cave. This character knowledge carries weight throughout the movie, as the group variously splinters and works together to escape. Shocks and jolts start before the central scare appears. And props to an all-woman cast that feels totally natural and not slapped together to achieve cheap feminist self-congratulations. Well-acted and atmospheric, I recommend this movie to anyone wanting to see a solid, scary horror movie that doesn't reinvent the genre, but definitely strays from the norm. PS: Don't bother with the sequel.