Actress Emily Blunt says that out of all scenes in the mystery thriller drama "The Girl on the Train", a sequence which was shot in a tunnel was most challenging for the film's team.Blunt, who essays protagonist Rachel in the film, said in a statement: "The tunnel sequence was really challenging for everybody. It was really cold and we were shooting in January and during night, it was like brutal.""But also we had to shoot tons of different ways of what you think you can see, but you don't see, the Mr X and the reality of what happened and how much to show of that, from different perspectives... It was such a complicated sequence to shoot for everybody."The tunnel scene unfolds the crux of the film, which has been adapted to the screen from a cult novel and is helmed by acclaimed director Tate Taylor and produced by legendary filmmaker Steven Spielberg.Its story is based on an individual who has succumbed to melancholy and has found her solace in alcohol, seeking happiness in fantasizing about the perfect life of a couple from her former husband's neighbourhood.The film has Rebecca Ferguson, Haley Bennett, Justin Theroux in the lead roles, apart from Blunt. It is releasing on October 14.