We found the Rubik's Cube behind some puzzle books, led there by clues around the Main branch of the library. Once solved (by taking it apart and reassembling it; we're not proud), a phone number circled the cube.

So went one of the puzzles in the Perplex City Live event held on Saturday in San Francisco, the first event of its kind in the U.S. Perplex City is a collectible card game, where you buy packs of cards and trade the duplicates with fellow solvers. (If you play, and want to trade cards, let us know.) Each card contains a brain teaser, and the full set of cards, plus the podcasts, the website, and various other clues, will lead you to a treasure buried somewhere in the world, worth $200,000. There's a complicated story behind the game, involving the fictional Perplex City, puzzle master Sente, and a terrorist organization known as the Third Power. The organizers framed the Saturday event as an attempt to re-establish a link to Perplex City after the Third Power destroyed the original one in London. The more puzzles we solved, the more likely the link would get re-established.