One thing I really love is swinging on a swing. Like, at a playground. It's so endearing and frivolous, and also a great time to reflect on things. I enjoy watching the scene around me change as I sweep a parabola through the air.
As a kid, I wasn't a very good swinger. It took me ages to get the hang of it, and I was always pretty wussy about going too high. Even now, after years of experience, it takes a while for my insides to feel okay about flying up and down. And at 27, I wonder if there's an age when it's no longer acceptable to swing. While playgrounds are the domain of children, swinging is enjoyable (and light exercise!), and it feels too arbitrary to simply stop. You needn't let things slide into an unrecoverable childhood nostalgia. Stay young at heart, you're never too old to have fun!