This tense thriller is a terrifying chronicle of six young women who explore caves in the Appalachian Mountains and find unspeakable horror thousands of feet down. A cave-in traps them with no way to retrace their steps, but don't yet know that a terrible fate lurks around the tunnel's next bend. The film is reminiscent of "The Lost Patrol" as the ladies band together as much as they can against a ghoulish and unseen foe, with each girl's nerves pushed to the breaking point. The movie's dark, claustrophobic look adds realism to the ghastly dangers that the young women face and the music score is effective. The girls have several encounters with the predators underground and use torches and climbing gear to fight off their attackers. Natalie Mendoza is the group's ambitious leader who misleads the other women about the caves and also tries to cover up an awful deed she committed in a wild flight to escape. The four other women on this ill-fated expedition are also good in difficult roles. This movie is certainly one of the best films of 2006.