"Puzzle" is the second track in the FEZ OST.
"This track evolved out of messing around with a new instrument I picked up at the time, called Synplant by Sonic Charge. It's got a real unusual but ingenious interface... if you're into synths I highly recommend checking it out. This song is a mockup of how the music behaves in the game. In game, this song is broken up into 27 individual assets, and plays phrases periodically, and moves through different keys depending on the time of day in FEZ."