Give your brain a workout on the type of brainteasers that challenge the best solvers at the World Puzzle Championships. They're tough, but fun, and the feeling of satisfaction you get when you succeed is simply unbeatable. Some of the puzzles are oldies but goodies, like battleships--and its many variants--where you search for a fleet hidden within a grid. In "Eminent Domain," try to determine which blanks cells are owned by the numbered ones. For "Hex Loops," locate a path that travels through adjacent hexagons: the trick is, it has to end where it started, and the lines can't touch or cross. From Snaky Tiles to Spiral Galaxies, these Mensa-level conundrums will get your mind in shape.