Find a path that visits every square in the grid, avoiding walls and never crossing itself, to create one continuous circuit. To get the hang of things, start with one of the simple 4x4 grids. Plot your moves carefully. Try to think ahead; not just by one square, but by four or five. If you think you've made a mistake, trace back over your line. It will disappear. If you really get stuck, press Hints. Any mistakes will turn red, then disappear. But if you're on the right path, we'll add a line. There's only one solution for every puzzle. When you find it, you'll know. Puzzles start with 4x4 grids and go all the way to 20x20. The bigger puzzles are very challenging and can take hours to solve. If you have to quit in the middle of one, don't worry: your progress is automatically saved. Many find working on these circuits meditative; others reach for the ibuprofen. But no matter which camp you find yourself in, know you're exercising your abstract thinking skills and challenging your brain in ways that actually matter. Inspired by a puzzle created by Irish mathematician William Rowan Hamilton in 1856, these circuits start off easy and get hard. Really hard. Good luck! Terms of use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/