Learn to dance

In a 21-year study of older adults, dancing was the only physical activity linked to a lower risk of dementia (more on why in cognitive reserve). Cycling, swimming and golf weren't. The likely reason: dance combines movement, music, memory for sequences and another person, all at once. Evidence: decent

That's one observational study, so hold it lightly. It's also exercise, time with your partner, and something you'll be terrible at for a month, which is good for you.