Running.

Creating/writing/producing music, playing somewhat chill MMO games (often solo), walking/hiking in nature/interesting urban areas I haven't fully explored before. Drinking a beer in late afternoon while out in nature, just letting my thoughts run wild. Those all get me pretty far and never drain me like extroversion activities do.

This is going to sound a little strange, but playing music on stage works for me. At least in moderation, and provided you aren't the lead singer/MC who has to interact with people. You just wanna be some guy in the corner jamming on whatever you jam on.

You kind of get the best parts of being in a social situation in terms of seeing new places, having interesting experiences you can ponder for days to come, and occasionally getting free food and/or a green room where you can veg out in isolation and no one expects anything of you. But you can avoid the negatives: having to make small talk, looking awkward with nothing to do and no role to play, being labelled antisocial, getting roped into some horrible activity you did not sign on for, etc.

And it turns out there are a lot of introverted musicians. You only really need one extravert in a band.