On the flat lava plain of Reykjanesbaer, Iceland, near the Arctic Circle, you can find the mines of Bitcoin. To get there, you pass through a fortified gate and enter a featureless yellow building. After checking in with a guard behind bulletproof glass, you face four more security checkpoints, including a so-called man trap that allows passage only after the door behind you has shut.
Quick! Where were you last Tuesday at 6:35 PM? If you're anything like me, your answer is probably along the lines of "I... have absolutely no idea." Most people's brains just don't work that way. But odds are, Google knows. They probably know where you've been most other days, too.