The house depicted in the film was used for day scenes only. It was torn down after filming because it didn't meet local building codes. The rooms were duplicated on an L.A. sound stage for night scenes.
The Crown Point Bridge appears throughout the film. It was located in Addison, Vermont, near D.A.R. State Park, very close to where the house was built. Filming closed the bridge for several days, causing problems for locals on both sides of Lake Champlain. The bridge closed permanently in October 2009, after an inspection revealed serious deterioration. It was demolished December 28, 2009, and is scheduled to be replaced by 2011.
Michelle Pfeiffer stated in interviews that she was initially put off by all the technical aspects of the film, but eventually learned to embrace them. In the end the actress found the experience both educational and enjoyable.
Robert Zemeckis consciously shot What Lies Beneath in the style of Hitchcock, if he had access to digital technology. Also, the heroine of the film is a blonde, which was a common trademark of Alfred Hitchcock's.
Robert Zemeckis had a replica of the house built. Five different versions of the bathroom set were constructed. So various parts of the same scene could be filmed at different times on opposite coasts.
Throughout the film, Claire's (Michelle Pfeiffer) eyes are more grayish, although they are blue. In the scene where Claire allows Madison (Amber Veletta) to posses her body, her eyes are a darker shade of blue. This is because director Robert Zemeckis wanted to emphasize the eye color change from blue to green so as to make it easier to identify the "change of character". Contact lenses were used to make this feature-change.
According to the script "What Lies Beneath" by Clarke Gregg, Claire and Norman Spencer were different to the way they are portrayed in the movie. According to the screenplay, Claire and Norman smoked pot and didn't have as close a relationship as they did in the movie. Their characters were changed to make the movie fit in better with the type of motion picture setting.
According to the original script "What Lies Beneath" by Clarke Gregg, the scene with the Ouija board was started by Jody, who later ran out screaming after the séance had gotten a little out of hand. The scene was changed for the movie in order to show how much Claire gets into the encounter with the ghost, and to emphasize how much Claire thinks she is losing her mind as Jody isn't as scared as she later is.
When Michelle Pfeiffer lies stunned on the floor and the murderer leans over her face, the camera seemingly cranes down underneath the floor to look directly up at her face. The effect was created by using a glass floor. The solid floor at the start of the shot is drawn in by computer. A glass floor is also used when she drops the keys later on.