Wonderfully shot, Tightly told, claustrophobic tale of a group of cave explorers trapped beneath the surface of the earth with some unknown horror. This movie is dark, foreboding and deeply creepy. The film-making is so terrifying at times that you feel like you're trapped in there with them. I found the performances to be superb across the board and the sense of dread that the director is able to build is truly something to behold. The film seems to suffocate you slowly, as if you were being drawn further into this subterranean hell with no discernible way out. The lack of the light and the hard source helmet-lamps that the director uses to light his actors, keeps the menace at the corner of the frames at all times. Any time a horror film can make you feel like the worst is yet to come, moment after moment, then that film is doing something right.