How long did it take to write the album "Physical Graffiti"?
Kashmir (song):  Included on their sixth album "Physical Graffiti" (1975), it was written by Jimmy Page and Robert Plant (with contributions from John Bonham) over a period of three years with lyrics dating to 1973. Physical Graffiti: Physical Graffiti is the sixth studio album by the English rock band Led Zeppelin, released as a double album on 24 February 1975 by their newly founded imprint label Swan Song Records.
over a period of three years