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.
I checked a few of the particulars against the production design retrospectives.