The main activity of any person's life, anyone and everyone, inextricably linked with personhood. To fully comprehend it, avoid thinking of yourself and others as female, male, partial gender, person of particular age or social rank, or species though in our case any readers are overwhelmingly likely to be human. The only defining characteristic of a person is sentience. We all live in a brief moment of existence looking out through the same barred window at the fantastic cosmos without and within, ineffectually watching, wondering, waiting.
The optimist protests, "But I have been to lots of places!" But a place is still a place with you in it. You look out your eyes, windows of the soul, at a prospect of the universe. There are three types of views: interior, exterior, and prospect. In the grand scheme the prospect changes not; only the local interiors and exteriors may vary. You have only ever been in one place, at one time.
In this age before interplanetary travel (if that age ever comes) nobody can leave the planet we're on, third from Sol, unless you happen to be one of a very small number, and even they don't go far and have to come back before long (if the blessed void doesn't take them).
Though you may travel far and wide upon the planet, almost all of your time will be spent among other people, relying on them for necessities, luxuries, society, companionship. Your relationships with others permanently occupies a significant share of your mind. Unless you happen to be a hermit in which case you probably aren't reading this. Your self-with-others is ever-present, like your self, trapped in reality, suspended in memory.
Where do you think you're going? There's nowhere to run, nowhere to hide. Is it nihilism? Is it solipsism?
It is an action. It is not something you do for lack of something better. It is the best thing you can do. It is the only real thing. Sit, lay, plug your ears, cover your eyes. Revel in the vacuum. Welcome to the place you have always been.