Motorcycle riding brings me peace. Being so focused on solely riding that you're able to clear your head of everything else. Feeling/hearing the engine, clicking down a gear and rev matching a downshift, planning your turn in and looking at your apex, twisting the throttle, etc. It clears my mind every time and for that I always leave with a smile on my face and a feeling of tranquility.
Driving is another, but specifically back roads in a sports car. Windows down, music off. The engine/exhaust note as the only soundtrack needed. A perfectly executed heel/toe downshift, getting on the throttle just a little bit early coming out of a turn with just the right amount of steering input and gradually rolling into the throttle to hear the car rip and bang the next gear. Lovely.
Less so now, but modding and working on cars. Planning a build and buying parts sucks time and leaves you poor. Wrenching on them is usually frustrating without a lift and proper tools, but that feeling you get when you're done with that day's project is always rewarding. Stand back and enjoy your work just the way you pictured it. That first start up after a new exhaust install, or the new stance after a suspension install is always a zen feeling.
As I've grown older, and slightly less selfish, it has become doing the things that the wife enjoys doing. I'm not much of a hiker or lover of nature, but knowing that hiking in the woods with our dogs is what brings her peace gives me some too. Making her laugh or bringing a smile to her face gives me great satisfaction.