[Serious] "Doing Brain-ups", how do you exercise your brain?

[Gawdzilla Sama]

I get cognitive function tests once a year, part of a study the VA is participating in. I'm not in the control group so researchers can suggest things for me do to try to stay sharp (some would say "get sharp") into my dotage. So I play games. Spider solitaire, with a win rate of about 3% in the hardest mode is one. Scrabble (online) is another. I also play the grand chess games, like Ages of Empires II.

If you haven't considered this aspect of your old age all I can say is "it's never too early."

Suggestions/thought/brickbats?