If you're looking for an exercise that's fun, interesting, and will work out your entire brain, grab an instrument and start playing.
Anita Collins at the TED-Ed YouTube channel explains what's going on in your brain when you jam out. When you play music, the entire brain lights up because you're using almost every region of the brain -- particularly the regions dedicated to audio, visual and motor functions. Naturally, those regions are strengthened as you practise and play your instrument more and more, and that leads to many benefits outside of music. These benefits include more attention to detail, stronger planning and strategic skills, and a better memory.
Not sure where to start? Don't worry, learning an instrument is very doable as long as you have the drive and are willing to put in the effort. You can even learn everything you need in the comfort of your own home. So grab an instrument you've always wanted to learn and get that brain working.