Most of 2007's "National Treasure: Book of Secrets" (starring Nicolas Cage) was filmed far from California, in locations such as London, Paris, Washington DC and Mount Rushmore.

But the houses of two main characters in the film (which are supposed to be in Virginia) were actually located in the Los Angeles area.

The first location, Nicolas Cage's house (where he is forced to break in, because his girlfriend locked him out) is none other than our old friend, Greystone Mansion, at 905 Loma Vista Drive (north of Sunset Blvd), in Beverly Hills.  Map.

Greystone is part of a public park and its grounds are open to the public. A number of movies and TV shows have been shot there over the years, including "Indecent Proposal", "The Bodyguard" and "Gilmore Girls". (Click here for more details.)

The second location is the home of Nicolas Cage's father (played in the movie by veteran actor Jon Voight).

It's a large colonial home, with distinctive round windows above the door. The director's commentary says it's in Pasadena, but its not.  It's actually in nearby South Pasadena (a separate city). A friend, Chas Demster, found this one for me, at 1030 Buena Vista Street, in South Pasadena.
(That's the first house west of Fairview Ave, on the north side of the Buena Vista street.)  Map.