Trivia: Ironically the evil cult in this film is almost the exact opposite of that from the games. In the games, the cult is a malevolent force, trying to give birth to their dark god, and the burning of Alyssa was part of an ongoing process to help summon it. In this film, they're essentially extremely fanatical Christians who are trying to cleanse what they view as "evil" and "ungodly" and the burning of Alyssa was done because she was seen as "impure" and in need of cleansing by fire.
Trivia: Director Christophe Gans wanted to use the original soundtrack recordings of Akira Yamaoka's scores from the various "Silent Hill" video games in the film. However, due to a legality issue necessitating the hiring of a Canadian composer for the film, Jeff Danna was selected to serve as the lead credited composer. However, it was later confirmed that he actually composed very little original music for the film, and instead mainly focused on created re-mixes and new recordings of the themes from the video-games, so that he and director Gans could preserve Akira Yamaoka's music and style as much as possible.
Trivia: In order to show Rose's progression as a character and her increasing desperation, her clothing slowly changes color throughout the film - going from a standard wardrobe of warm colors to a dark, almost blood-red by the time the film is over. Clothing in dozens and dozens of subtly different hues was crafted for the film, with the actress frequently changing wardrobe several times a scene. The changes are so subtle, that they're near-impossible to notice in any given scene.
Trivia: Director Christophe Gans originally didn't want any men in the film whatsoever, as he wanted the movie to be heavily inspired by witchcraft, which is traditionally viewed as being somewhat more feminine. Writer Roger Avery also half-jokingly-half-seriously suggested in an interview that Gans has a "thing" for American women, and wanted to make a film with nothing but women from the US and Canada. The male characters were added into the film as a studio-note, as executives felt it was a bit odd that there were no men in the early drafts of the script.
Trivia: In the opening scene, when Rose runs under the bridge, she passes some graffiti tags. One of the tags has the name "Cheryl." In the original video game, Cheryl was the name of the daughter the main character is trying to find. For whatever reason, the name was changed to "Sharon" for the movie adaptation, but they threw in the graffiti tag as a nod to the game.
Trivia: The character Alessa in the original video-game is often theorized to be a reference to Stephen King's "Carrie," as Alessa possesses some psychic abilities similar to the titular character of that novel, and the game has a number of other King-related references. Jodelle Ferland, who portrays Alessa as a child in this film, coincidentally also briefly portrayed a younger Carrie White in flashbacks in the 2002 TV-movie adaptation of "Carrie."
Trivia: Director Christophe Gans was a massive fan of the original video game, and spent five years slowly gaining the film rights from the game's distributor Konami.
Trivia: The film's interpretation of the town of "Silent Hill" is loosely based on the town of Centralia, Pennsylvania, which had to similarly be almost entirely abandoned after an underground coal-fire occurred, which is still burning to this day. People who visit the remains of the town often leave graffiti tags behind that allude to the town being the real-life "Silent Hill." (The words "Welcome to Silent Hill" being particularly popular for people to write on the roads).
Trivia: Director Christophe Gans is friends with actress Deborah Kara Unger in real life, and desperately wanted her to play Dahlia. When he approached her for the role of Dahlia, he was sure she would be offended, as Dahlia is meant to be frail, older and in poor shape. He lead the conversation with "Please don't slap me." To his surprise, Unger was delighted by the role, as she'd been wanting to play an odd, eerie character like Dahlia for some time.
Trivia: In the original ending, rather than Alessa killing off the cult with the living strands of barbed wire, dozens of "Red Pyramids" were going to appear inside the church and slaughter them, as they are meant to represent the town's old executioners in the context of the film. This idea was scrapped early on for practicality and budgetary reasons.