10 PERFECT Monster Movies You MUST Watch

In Neil Marshall's The Descent, Sarah goes spelunking with her friends in a mountain cave to help deal with her grief, only to get lost. While the group dynamic starts breaking down, Sarah discovers the cavern is populated by flesh-eating troglodytes called Crawlers.

Even though the Crawlers look haunting, it's the unknown factor surrounding them that magnifies the scares. Sarah and her friends are constantly wandering around aimlessly in pitch-black, oblivious to how close or numerous the Crawlers are. Even when the group use night-vision goggles, the Crawlers evade detection by hiding on the walls and ceilings, so the characters (and viewers) don't notice them until it's too late.

Themes of remorse and guilt are apparent before the ensemble step into the cave, compounding the claustrophobic atmosphere long before the Crawlers show up. Rivalries and betrayals make the group gradually implode, so the threat comes from within as much as from the creatures. Rather than painting Sarah and her companions as heroines, they're perceived as flawed human beings who'll perform immoral deeds to stay alive.

And if you're watching the UK version, the original ending should leave anyone with a lingering sense of hopelessness and defeat long after the credits roll.