Screen legend Robert De Niro has managed to keep a low profile while making "The Dark Fields" here. Since Monday he's been shooting on the 34th floor of the Loews Hotel (12th & Market). While co-star Bradley Cooper's been spotted around town for the past month, De Niro seems to only be seen by workers at City Hall, where the movie's trailers are parked. We're told the star is commuting from his New York home. The film is shooting today outside at 16th & Market Streets.