"The Wanton Song" (Led Zeppelin)

At first blush, there doesn't seem to be a lot going on in "The Wanton Song," a track from Physical Graffiti (1975) that came about as the result of an impromptu jam during a soundcheck on the band's 1973 tour.  Jimmy Page just plays the same two notes, an octave apart, over and over.  And Robert Plant delivers one of his less subtle and more reptilian sets of lyrics.  There's no mysticism or references to Tolkien lore, only slightly poetic references to shagging groupies.  (Like the song "Sick Again" from the same album, it's an illustrative snapshot of 70s hard rock excess on the road.)
But there's just something about the simplicity and raunch of Page's riff over the dripping funk of John Bonham's drums and John Paul Jones's bass.  It creates a hypnotic effect that somehow never grows stale, even after repeated plays.  (I know, because I listened to the song on repeat for a solid 3 hours once when I was working on a web design project in college.)
There's also something electrifying about when the band moves in unison through the series of complex (almost jazz-like) chord changes from the grimy verses to the sparkling instrumental choruses.  Page's guitar fed through a rotating Leslie speaker almost sounds like chirping birds greeting a brand new day, which I think fits the theme of the song pretty well: whatever hormone-fueled mistakes took place the night before get erased with the light of each new day/each new face/each new city.
And the wheel rolls on...