Okay, so this is a bit of a blanket we've thrown over the exercise section of what might be considered a hobby. But it really doesn't matter which form of exercise you take up, they'll all promote a smarter you.
A healthy body which gets regular exercise will result in flow on effects fro the brain. The relationship between the two should not be underrated.
It's all about better circulation. Better blood flow to the brain means better ideas flow through it.