The 2nd best way to exercise your brain.
Dialogue with others. Language and the human brain coevolved with each other, allowing us to excel over many of the physical and mental skills of other mammals and primates. If we don't exercise our language skills large portions of the brain will not effectively interconnect with other neural structures. Dialogue requires social interaction , and the more social ties we have, the less our cognitive abilities will decline. In fact, any form of social isolation will damage important mechanisms in the brain leading to aggression, depression, and various neuropsychiatric disorders. Just don't let yourself get trapped in angry dialogue as irritable conversation will do considerable damage to your brain. Instead talk about abstract ideals like harmony and peace. Ask what your neighbor thinks of evolution and the Big Bang !