the mansion used in sunset boulevard, (as well as rebel without a cause), was the old William Jenkins residence located at 3810 wilshire boulevard at crenshaw.
the house and the garage are visible on the left side of this 1934 photograph
USC Digital Archives
in this 1930 aerial, the house is located at the center bottom of the photograph
USC Digital Archive
the house was demolished by J. Paul Getty in 1957 to make way for his Getty Oil headquarters. Now it is the glumly nondescript Harbor Building.
all interior scenes from the movie were actually filmed on location inside the house.
the swimming pool was built for this movie, and was in fact a non-working swimming pool, as it was not equipped with any filtration system.
i wish you all the best on your upcoming eye surgery