From flooded passages lit by headlamps to urgent voices echoing off cramped walls, the director of "The Cave" -- the first big-screen retelling of Thai rescue operation -- promises to capture the peril of the mission when it premieres at Busan International Film Festival.
"No one is going to say, 'Oh that looks like a set'," Thai-Irish filmmaker Tom Waller told AFP ahead of the Saturday debut at Asia's biggest film festival in South Korea.
"Those who suffer from claustrophobia, there should be a warning... (you) might get a little bit anxious," he joked.
The 2018 mission to extract 12 young Thai footballers and their coach -- known as the "Wild Boars" -- from Tham Luang cave in northern Thailand captivated people around the world.
After wandering into the complex during the rainy season, the team were trapped by floodwaters for 18 days before they were sedated, fitted with masks, and dragged to freedom through kilometres (miles) of narrow passageways.
Waller's challenge: to recreate the conditions of the dank, dark environment that made the rescue of the "Wild Boars" so harrowing and unprecedented.
To do so he filmed in similar caves around Thailand and employed four of the rescue divers to star as themselves.
"We had to deal with snakes, huge spiders," Waller said.
The movie is hitting theatres ahead of bigger and better-financed projects, and he hopes the festival will give the independent film the profile it needs to go truly global.
"Us being shown at Busan first, it's playing the film on a world stage," Waller said, adding that it will debut in Thailand in November after a festival tour.
Appetite for the incredible tale remains strong more than one year after the operation as companies pump out books, shows, and documentaries.
In the pipeline is a Netflix production from the producers of "Crazy Rich Asians" for which the rescued footballers were reportedly paid $100,000 each.
National Geographic is stepping into the competition with a documentary by the team behind the Oscar-winning film "Free Solo".
But Waller's film will have the advantage of being first to screen, and is taking a cinema verite approach.
Four divers from Canada, China, Finland, and Belgium are acting in it under their real names, as is an American journalist who covered the saga.
Ireland-based Belgian diver Jim Warny, who helped pull the team's coach out, said he had a flashback when they recreated the scene.
And he wants the film to inspires others to dream big.
"I was afraid in the cave, I'm always afraid when I go cave diving," he said.
"I see it as a duty to show people that they can do amazing stuff against the odds."