A number of years ago, I can't remember exactly when, I began to worry about cognitive decline, so I started doing Sudoku puzzles regularly. I had never learned how to play, but once I got the hang of it, I fell in love. Beyond just getting my brain to work, I found that the techniques I used to solve sudoku puzzles started to show up in everyday life. 
 
Sudoku is simple deduction, but it also involves moving forward when you don't have all the answers. This is a handy skill. We can often get stuck because we don't know the solution to a problem, but not knowing the solution is not the same and not knowing how to proceed. This might sound obvious to some people, but it has been helpful for me. 
 
For example, you don't know exactly where that "5" is going to go, but you know it's going to be in the center column. And that not only means you know roughly where the "5" will go, you also know with certainty where it will not go. So you can place the other numbers and worry about the "5" later. 
 
Similarly, you might not know exactly where people should sit at your dinner party, but you know Uncle Drewfus can not sit at the same table as cousin Elmer because of their radically different perspectives on cilantro, so at least you can seat them far apart and the rest will fall in place later. 
 
Am I making any sense? 
 
Regardless, Sudoku is awesome and now you can solve puzzles wherever you go because these books are small and cool and fun. There are 36 puzzles in three levels of difficulty. Two cover options: Light Tan and Red Red (same puzzles). 
 
Enjoy.