London, England (CNN) -- Martin Scorsese found himself scaling rocks early one morning while making his latest movie, psychological thriller "Shutter Island."
"Actually, I was rock climbing at one point at seven in the morning, which was quite unique," the 67-year-old director said.
It's an experience that, like all his movie-making, Scorsese likens to a battle.
"Once you're in the thick of battle, you just try to get through it," he said. "By the second or third week of filming, you want to literally survive it."
Survival has long been an issue for the eminent "Taxi Driver" and "The Departed" director: Severe asthma kept him indoors for much of his childhood.
Film offered him a window on to the world: "I used to love westerns because you could see the outdoors," Scorsese said recently.
"It was fantastic but I could never go there," he continued, referring to the landscapes in films like those made by 1950s noir director Anthony Mann.
This time, Scorsese has fully embraced the elements. Pelting rain, ominous fog and dense forests play a crucial role in manufacturing the creepy atmosphere in "Shutter Island."
It stars Leonardo DiCaprio as Teddy Daniels, a U.S. Marshal investigating the disappearance of a patient from an asylum located on a remote island.
The film, a complex character study that pushes emotional boundaries, is Scorsese's fourth collaboration with DiCaprio. Their working relationship is going on a decade now.
DiCaprio said the role is perhaps his most demanding ever. "This is maybe the most challenging one to date for me, physically yes, but emotionally more so," he told reporters in London.
"Shutter Island" is full of sinister undertone and plot twists and turns, a throwback to old Hollywood genre films.
Scorsese said he first connected to the emotion of the thriller, which is based on a 2003 novel by Dennis Lehane. "I felt empathetic for the character, overwhelmed by the nature of the story," he said.
He found a door into telling that story, he said, through the "vocabulary of cinema's past and the nature of gothic literature." He paused and continued: "I don't know how else to tell the story except to utilize that vocabulary -- the rain, the darkness, the mansions, the framing."
Often hailed as the greatest living American director, Scorsese said he thrives on his job. "I need to work, I like to work," he said.
He's been making movies for more than four decades, which has resulted in a body of bold films, from the gritty "Mean Streets" (1973) to Hollywood spectacles like "The Aviator" (2004).
He finally garnered a best director Oscar for 2006's "The Departed," a win considered long overdue by many.
Going in to "Shutter Island," which was shot at an abandoned hospital for the criminally insane in Medfield, Massachusetts, he knew what atmosphere he wanted to achieve.
The mood and tone "was in my head, in my blood in a way once I decided to make the picture," he said.
Bringing the film to the screen was a constant process of finding his way in the mood so he could "choose, select, emphasize certain visual elements and sound."
As much a movie fan as he is a master filmmaker, he turned to several Hollywood classics for reference points when making the dark thriller.
An element of genre filmmaker Samuel Fuller's 1963 film "Shock Corridor" was always "hovering around the picture" because "it's in us, it's in me," he said.
He also screened, among others, Otto Preminger's "Laura" (1944) -- to get a sense of "the war-torn, war-ravaged hero"-- and Jacques Tourneur's "Out of the Past" (1947) for DiCaprio and co-stars Mark Ruffalo and Ben Kingsley.
To pull together the imagery, he enlisted the help of cinematographer Robert Richardson and production designer Dante Feretti, his long-time collaborators.
The end result is a cinematic puzzle. The film has a level of ambiguity throughout, DiCaprio said, that could lend an audience to have a different experience on further viewings.
"We were conscious that we were doing a film that could have a different interpretation the second time around, that could take on different meanings," he said.
The line where reality starts and dreams begin is blurred from the opening scene, appropriately a shot of a boat coming through the fog.
"I think it's interesting," Scorsese said of the scene, which he said is one of the key images of the film. "It's breaking through the mystery or maybe it stays in the fog. You don't really know."