Watch this in a pitch-black room for the full effect. Just make sure you aren't afraid of the dark.

While many initial copies used AVC (H.264) , there was a documented manufacturing variation where some discs were released using MPEG-2 encoding. Aspect Ratio: 2.35:1 (Widescreen).

: A tunnel collapse traps the women deep underground, forcing them to find a new exit.

Before any monsters appear, the film masterfully uses the environment—tight spaces, darkness, and the threat of being buried alive—to build unbearable tension. Technical Execution

Note that this 2007 film is distinct from the 2005 horror film The Descent