This is all 32 of JS Bach's Goldberg Variations, and two Well Tempred Clavier pieces, performed by Glenn Gould, played together, with the longest first and them all ending together at the same time.
I really like this piece, its a personal favourite. I like the way it sneaks up on you. I have posted it here specifically because the Soundcloud bot just isn't having it:
"Our automatic content protection system has detected that your sound "Goldberg Variation" may contain the following copyright content: "Goldberg Variations, BWV 988: Variatio 25 a 2 Clav." by Glenn Gould, owned by Sony Classical. As a result, its publication on your profile has been blocked."