 When George Lucas (qv) met with Steven Spielberg (I) (qv) to  discuss a third Indiana Jones movie, he wanted to have it set in a  haunted mansion. Spielberg had just finished  _Poltergeist (1982)_ (qv) and decided that he wanted to do something  different. Lucas then came up with the idea of the Holy Grail and  Spielberg added the idea of a father/son sub