I have just been spending 4 hours on a 4x4 Sudoku puzzle where I here after 4 hours sitting in front of the computer find that I have made a mistake and can't find room for the 5 that needs to be somewhere in a quadrant. I can identify in which quadrant the mistake is, but I end up figuring that 4 hours is enough time spend on this.
Sudokuy is really very fascinating, the 3x3 is usually solved in less than 30 minutes, it is a nice way for me to relax, but I have only once had the patience to solve a 4x4 sudoku, that took me something like 4 hours back then.
I have made myself a little programming task of making a Sudoku program of some kind, Sudoku is something that computer programs are much faster at solving than a human brain will probably ever be ... at least if you have anything that resembles as much computing power as what has the everyday person has easily been able to get for the last ~25 years.
Still to make this program I need to learn Java better which right now is the language I am trying to motivate myself to get learned, it's been months since I last did spend time with this, it will probably have to wait until winter like so many other projects involving a lot of sitting down.
Right now I am out working a lot in with geophysics and related things which has me very physically active, if I was to sit down to much now I would get out of shape, it has been hard enough to get myself into physical shape again after the winter, I am kind of planning not to allow myself to get as much out of shape again like I did last winter.