I would suggest travel over most of these. Particularly if you live in a fairly inward looking society like the US. Forget SF - live in another country, learn a

I would suggest travel over most of these. Particularly if you live in a fairly inward looking society like the US. Forget SF - live in another country, learn another language while your brain is still plastic enough to become truly fluent, understand your own culture by spending time among others, realise how fortunate you are to be born in a developed country.