Leonardo DiCaprio

Leonardo DiCaprio truly had a terrifying working on 'Shutter Island'.

The film follows a U.S. Marshal and his partner travel to a remote insane asylum to find a missing murderer, only for the sheer horror of the criminal's deeds to begin to chip away at their sanity.

Leonardo admitted working on the picture was "traumatic", and called it "one of the most intense, hardcore filming experiences [he's] ever had".

He continued: "I went to places and unearthed some things that I didn’t think I was capable of. It was like an emotional layer cake that just kept getting deeper and deeper."

The movie star also revealed the nightmarish plot points of the flick began to seep into his dreams.

He said: "It took me back to the one time I really remembered my dreams, because I usually don’t.

"But when I used a nicotine patch when I was trying to quit smoking, I did have bloodcurdling nightmares of mass murders, and I woke up in the middle of the night and had to take the patches off. I guess I had moments like that in the film."