I like logical puzzles, anything from learning how a language works to sudoku to designing (or reverse engineering) complex mechanical systems, such as autoloading firearms, helicopter rotor arrangements, CNC machines and basic machining tools (lathes, etc), and even some benign things like doorknobs, house ventilation systems and vacuum cleaners. Designing things is how I got into programming, I wanted to study engineering in college and there was only a CIS course available (other than nonsense EBA or EC degrees). After the first programming course I could already see how it would make my life as an engineer so much easier, making advanced calculators and such in the console. Now I'm starting to really get it with the code, and I'm finding all sorts of 'inventions' and cool 'machines' that have already been invented by others that I could never have found in a purely physical world, things like data mining programs or the linear algebra transformations that end up as 3d on a computer screen.