Wilson Salazar, who plays the Messenger, was an actual soldier of the FARC from 11 to 24. Director Alejandro Landes found him at a reintegration program and hired him initially as a consultant, before deciding to cast him in the film as well.
The jungle scenes were shot around the Samaná river, five hours from Medellín. Because of the conflict, the place was visited only by soldiers and illegal gold miners until recently, hence remaining mostly unspoiled by humans. For the cast and crew, mules carried food and gear and a family of gold miners built military tents.
The mountain scenes were shot in the Chingaza National Park, which is about a four-hour drive outside Bogotá and more than 13,000 ft (4,000 m) up.
The film is loosely based on William Golding's Lord of the Flies. The severed head of a pig appears in the film as an homage to the novel.