If you are shooting a film about a group of women trapped in an unmapped cave system, the intuitive, independent approach would be to find a real cave. It seems cheaper and more authentic. But director Neil Marshall and production designer Simon Bowles understood the fatal flaw of location shooting: rock does not yield to a camera crew.
The Soundstage Cave
For The Descent, they made the counter-intuitive decision to shoot the entire film on a soundstage at Pinewood Studios. Bowles constructed a modular, highly detailed cave system out of timber and scaffolding. He painted the sets to look wet, slick, and suffocating.
This required a significant portion of the £3.5M budget, but it solved the ultimate logistical nightmare. You cannot easily light a real cave without making it look like a tourist attraction, and you cannot safely move actors through dangerous crevasses while maintaining a shooting schedule.
Modular Claustrophobia
Because the walls were fabricated, the production could physically reconfigure the sets on the fly to accommodate dynamic camera angles. They could remove a wall to get the lens exactly where it needed to be to make the audience feel trapped alongside the characters. By completely controlling the environment, Marshall engineered a level of claustrophobia that would have been impossible on location. He proved that the ultimate tool for achieving grueling, psychological realism is sometimes complete artifice.
Insights regarding the modular cave sets built at Pinewood Studios were synthesized from production design retrospectives.