Neil Marshall (Dog Soldiers, Doomsday) came along pretty much out of nowhere with this monstrously scary tale of an all-female cave-diving group who get lost inside an unknown cave system. With nowhere to go but further down in order to look for a way out, things go from bad to worse when the ladies come up against some nocturnal monsters. Aside from the unique aspect that the film has an all-female cast, the brilliance of the film is how its utterly terrifying before the actual monsters show up, with amazing use of tension and conjuring a deeply uncomfortable feeling of claustrophobia a scene in which one of the women is trapped and has to squeeze through before some rocks collapse is heart-in-your-mouth tense. Then, of course, the "Crawlers" pop up and add a whole other terrifying dimension. Its a masterful film that does everything a horror should and more, providing that rarest of things: a genuinely scary experience happening to characters about whom you actually care. For me its the high watermark of modern horror that has yet to be bested. Which of these horrors are your favourite? Did I miss off any essentials? Share your thoughts in the comments below.