Smiley Smile by The Beach Boys. Though I didn't yet know SS was a mere hint of what the album originally entitled Smile was to have been (which I learned in a 2-part story on the album in Crawdaddy magazine, the article later included in the author's book Outlaw Blues, by the great music critic Paul Williams), there was enough there to blow my little 17-year old mind.
Though Brian Wilson didn't finish Smile in 1967 (it's a long story, which a search will lead you to), what he had completed was finally stitched together in the early 2000's (2003, iirc) and released by Capitol in several forms, the most complete being a big ol' boxset. Smile is quite unlike any music you have ever heard, I guarantee you. Van Dyke Parks was Brian's collaborator on Smile, and his first album---Song Cycle---is another stunning work of art.