Twisty puzzles, such as the Rubik's cube. Just to start with the basic Rubik's cube itself, there are a lot of ways to enjoy it. There are competitions for solving in a variety of different ways, from the standard speed solving, one handed, blindfolded, or fewest moves. Then there are tons of different puzzles that you can get, perhaps even hundreds of different ones. They can be different shapes, have different number of layers to turn, or turn in unusual ways. It can be fun and relaxing to get a new puzzle and figure out a solution by yourself.