Twenty-one separate cave sets were built for the film. These were carefully reused with different camera angles, set dressing and lighting to suggest a nearly endless collection of interconnected tunnels and caverns. For realism, the makers often limited the lighting of the sets to light sources that the protagonists brought with them, such as flashlights, helmet lights and light sticks.
The filmmakers considered it too dangerous to film in an actual cave. It also would have been far too time-consuming, so they opted to build one instead.
Production on this film was fast-tracked so that the movie could be released before the similarly-themed American film La cueva (2005). Unfortunately, it opened in the same week as the 2005 London bombings, which considerably hurt the film's chances at the box-office.
According to the audio commentary on the special edition DVD, there was an exact replica made of Nora-Jane Noone and after the movie was finished, she got to keep the head of the doll. Once, she put it in her mother's freezer as a joke.
Neil Marshall shot many of the crawlers at 18 frames per second with a 45-degree shutter to give them a "staccato movement."