I've always been an amateur astronomer. I by no means consider myself well-versed on the subject, but I can go out at night and point out the major constellations as well as being able to refer to many of the visible stars by name. I also know the locations for some of the deep sky objects (nebulas, etc) and have dabbled in photographing them. When conditions are right I like to point out M31/The Andromeda Galaxy to those who don't know and describe what they are seeing, "That small, fuzzy spot is an entire galaxy." Then I hand them a good pair of binoculars and let them take a better look at it. Its always a crowd pleaser.
Geology has always fascinated me. I wish I was better educated on the subject, but I know enough to make my rockhounding that much more fun. And I am learning all the time.
Hiking is a life-long love of mine. Did a lot of serious backpacking when I was younger and I've dabbled with the idea of getting back into it as I get older. But day hikes will always be a part of my routine, particularly hiking to the tops of mountains. I have always been enthralled by reaching a new summit that I haven't stood on before.
I was raised riding motorcycles (dirt bikes). Even did some racing in my youth (desert racing). Rode a bike to work for many years in my late 20s/early 30s. Kinda got away from it the last 15 years or so though. Still theres nothing quite like the feeling of freedom you get when zipping along on a motorcycle.
I've never been an avid birder but I do love sitting and watching them, especially when I have some nice quiet time alone in nature (as I often do, I camp and hike solo a lot). And I know just enough about them to make a semi-educated guess at what most of them are.