Though the film takes place in Mexico during the summer, it was shot primarily in Australia during the winter. Heavy coats were provided for the actors in between takes, and water and olive oil had to be sprayed onto their bodies to simulate sweat.
The female corpse discovered inside the temple by Amy and Stacy is intended to be the same character seen screaming for help at the very beginning of the film, but the living character and the corpse were played by different actresses.
In the novel, there are no "ruins" to speak of, just a hill overgrown with the vines and the shaft cut into it. Director Carter Smith suggested changing it to an ancient Mayan temple, an idea with which writer Scott B. Smith agreed.
The Mayan temple was made up of three separate sets. The first was the facade overgrown with vines for the characters to walk up. The second was the top of the temple, where the majority of the film takes place. The third set was used for the underground shaft and tunnel scenes. Shots that show the entire temple from a distance were a blend of the sets and CGI.
The trivia items below may give away important plot points.
Even though the novel and the screenplay were written by the same person, the deaths of the characters are switched around. In the film, Stacy cuts her knee and the plants start growing inside her. She ends up killing Eric and begs for the others to kill her. In the book, it is Eric who cuts his knee, and he kills Mathias. In the film, Mathias breaks his back and later gets his legs cut off. In the novel, this happens to Pablo (who is called Dimitri in the film). In the film, Jeff is killed by the Mayans trying to save Amy so she can escape. In the novel, Jeff is killed by the Mayans trying to escape after Amy has been killed by the plants during the night. In the novel, Stacy is the last survivor. She commits suicide in front of the ruins to warn off others who might find the ruins. But the plants make her body disappear. In the novel, Amy is the first character to die. In the film, she is the only one who survives and, unlike any of the characters in the novel, she actually manages to escape.