Greystone is the largest mansion in Beverly Hills (and that's saying something) and is probably the only one accessible to the public, at least partly.
Oil tycoon and Teapot Dome scandal figure
Edward Doheny built the 55-room Tudor style mansion/castle in 1928 for his son, who later died here in a murder-suicide only 6 months after moving in (he was the murder.)
Greystone Mansion and Park is now a Beverly Hills city park. The 18.5 acre grounds are open to the public. The interior is occasionally open for chamber music and theater presentations. Rooms in the mansion are rentable for filming, weddings, or other events. The views from the huge parking lot above the grounds are said to be spectacular.
Some of the movies filmed here in whole or in part include "Indecent Proposal", "The Big Lebowski", "Town and Country", "Air Force One", "Batman & Robin", "The Bodyguard", "Death Becomes Her", "The Phantom", "Nixon", "Heat", "Forever Amber", "The Fabulous Baker Boys", "Ghostbusters" I & II, "Stripes", "What Women Want", "The Witches of Eastwick", and "X-Men".
TV shows include "Dark Shadows", "General Hospital" (Luke & Laura's wedding), "Murder She Wrote", "The Winds of War", and "Dynasty Reunion".
Other notable events that took place here are the filming of Elton John's video "I Want Love" starring Robert Downey Jr.; actor James Woods was married here, and Kirk Douglas & his bride of 50 years renewed their vows here in 2004. President Bill Clinton held fundraisers here in 1999 and 2000. The site is also used for the annual Beverly Hills Garden and Design Showcase.
More info (including rental rates - invite me!

) at this
City of Beverly Hills page.
trivia: the video featuring Robert Downey Jr. lip-synching Elton John was shot in one continuous take, without edits