My tutor at Cambridge, Professor Nick Hammond, authority on the history of ancient Macedonia and on the life of Alexander the Great, used to coach me on what he called “exercises of the mind.” He knew I played tennis for the University and he put it to me that just as I trained hard for the tennis so should I stretch to exhaustion the muscles of the mind. Once he gave me to read Immanuel Kant’s Critique of Pure Reason and to read it again until my brain could at least begin to make some sense (not much I confess) of its hard and complex ideas.
A full life, he also told me, involved extensive exploration. In youth this might very well mean setting forth to experience lands and cultures far and wide. But as important was travelling within merely the circumference of your skull and that never ended. He was right of course. Before long, explorations in the mind become more important than travelling in the flesh.
New destinations abound if one reads enough.