Hey guys, curious if anyone had found some good activities that are the mental equivalent of lifting weights. What do you do say 15-30 min a day that gets your more focused and sharp?

I've toyed around with meditation, used to love playing chess, even walking dog sometimes can be relaxing and I found helps the mind. Sometimes I even take a walk simply to walk and think (I call it "walk the mind"). Also reading every night before bedtime at a minimum, plus has all other benefits of accumulating knowledge and enriching the mind. Anything else you guys found helpful?