"Yes, there are two casts you can go by, but in the long run - there's still time to change the pod you're on . . . "

IV, Zoso, Four Symbols . . . whatever you call it, Led Zeppelin's fourth album is ubiquitous with rock music. After the mixed reception to their third album, the band was on a mission to put out their best work yet. They hunkered down at Headley Grange, a creaky mansion in the English countryside, and produced an LP that would go on to become one of the biggest selling of all-time.

Unlike its predecessor, Led Zeppelin IV received near-universal praise. "Stairway to Heaven" became a timeless classic, perfectly melding the band's acoustic and electric sensibilities. "When the Levee Breaks" transformed an old blues record into an otherworldly sonic trip. "Black Dog", "Rock and Roll", "Misty Mountain Hop" ...