Challenge your reflexes and mind. Play Sudoku or do a crossword while pedaling slowly on a stationary bike.
Try reciting poetry while taking a walk.
At work, sit at your desk, and rotate your foot clockwise. Now, try to draw the number six in the air. Your foot will naturally change direction, so it will be difficult! It's easier if you use opposite sides of your body.
Change up your routine. Do regular tasks with the opposite hand. Put toothpaste on your toothbrush, brush your teeth, turn on the faucet -- all reversed. See how many times it takes to get it right. It may be challenging, but it's opening up new pathways in your brain!
The key to these brain games is to play mind games while also moving your body.