Los Angeles is famous for its modern architecture. Below are some great examples worth visiting:  

• The Bradbury Building. 304 S. Broadway at Third Street, Downtown LA
  Inspired by a science fiction novel, it features a century-old brick façade and a sky lit atrium. It also appeared in the movie “Blade Runner."
• Spadena House, “The Witches House”. Walden Drive at Carmelita Avenue, Beverly Hills.
  Originally built as a movie set, it was later moved to its present site.
• Mann’s Chinese Theatre , 6925 Hollywood Blvd., Hollywood
  El Capitan Theatre, 6838 Hollywood Blvd., Hollywood
  Pantages Theatre, 6233 Hollywood Blvd., Hollywood
• City Hall. 200 N. Spring Street. Designed by Albert C. Martin Sr.
  Until 1957 the only building that was allowed to exceed the city’s 13-story height limit.
• Getty Center. 1200 Getty Center Drive, Los Angeles.
  Designed by Richard Meier, this museum houses an impressive sculpture collection as well as Van Gogh's Irises.
• Walt Disney Concert Hall. 111 S. Grand Avenue. 
  Designed by Frank Gehry, the home of the Los Angeles Philharmonic.
• Watts Towers: 1727 & 1765 E. 107th Street, Watts
  Consists of nine major sculptures and are the work of one man, Simon Rodia.
• Chiat/Day Ad Agency. 5353 Grosvenor Blvd., Los Angeles
  House built in shape of a giant set of binoculars. By Claes Oldenbrug.
• Capitol Records, on the corner of Hollywood and Vine, is an iconic landmark.
• Castle Green, 99 South Raymond in Pasadena. Built as a hotel in 1888, this combination of Moorish, Turkish and Victorian architecture is now an apartment complex.
  
• The Barnsdall House, Hollywood Blvd & Vermont (1924)
  Designed by Frank Lloyd Wright for an LA artist/socialite.   Tours are available.
• The Gamble House, 4 Westmoreland Place, Pasadena (1908)
  Designed by Greene and Greene for a member of the Gamble family, of Procter and Gamble fame, this is a foremost example of Craftsman architecture.
• The Ennis House, 2607 Glendower Ave. Hollywood, built in 1924
  The most monumental of Frank Lloyd Wright's concrete block houses, it has the effect of a Mayan
  temple on a hill.  It was also featured in the film BladeRunner.
• Wayfarer's Chapel, Portugese Bend, Palos Verdes. Built in 1951
  Designed by Lloyd Wright, son of Frank Lloyd Wright; a unique all- glass chapel covered with vines.
• The "Chemosphere House", 776 Torreyson Dr, Hollywood Hills
  Designed by John Lautner. Looks like a flying saucer on the edge of a cliff.
• The Trianon Building, 1750-1752 N. Serrano Ave.  (One block East of Western and one block North of Hollywood)
  Built by Mary Pickford and Douglas Fairbanks Jr. in 1927 as an apartment building for actors and actresses.  It was designed to be close to the Franklin Ave. trolley and the Hollywood Blvd. Trolley. 
• Union Station remains a major rail transportation hub and architectural wonder.
• Griffith Observatory is an impressive observatory located in a bucolic park. It was featured in a climactic scene in James Dean's Rebel Without a Cause.
• Huntington Library in San Marino/Pasadena area has the wonderful home of Railroad builder Huntington, libraries (including the Blue Boy and Pinky Picture), wonderful gardends (including Japanese, cactus, sculpture, and other gardends.)