The visual effects of the film are incredible and unique because when people from different worlds are in the same room, one must be standing on the ceiling and one must be on the floor, depending on how the audience sees it. This visual effect creates a world that no audience has ever experienced. According to Jim Sturgess, this was sometimes difficult to work with. His role required him to work very hard physically, and during filming he dislocated and fractured his shoulder when doing a particularly challenging stunt.

Juan Solanas got the idea for the movie from an image he saw one morning in his mind of two mountains, opposite each other. On the lower one, there was a boy looking up at a girl, who was upside down on the upper one, looking down at him. The image fascinated him, but he was unsure whether he would make another movie. But after the story came to him, Solanas became very excited about the making the very ambitious movie. He wanted to make a big “fairytale about reality.” He felt that shooting the movie so that the actors could act together in real time was very important and would give the film an organic quality. “Acting is reacting,” Solanas said, as he compared acting with another person with acting with a prop like a tennis ball, which is a method that is often used in movies with a lot of visual effects.