One science I've never really studied is geology. I developed an interest in it when I started hiking the Colorado Plateau area a couple of decades ago. So I can kind of pretend to knowledge about things like Navajo sandstone (a dramatic cliff-forming layer you see in the Escalante region and in Zion), while not actually understanding too much.
This last trip, we hiked Yellowstone and the Tetons, and one of my friends asked me a question about the geology that I could not answer. I did then get a book on the geology of the region, but also resolved to learn more about it in general.
So I turned to my old source, The Teaching Company, which is clearly trying to rebrand itself as The Great Courses. I'm currently watching and enjoying an introductory geology class, Nature of Earth. I now know something about the nine kinds of silicates that make up igneous rock, about oceanic basalt and continental granite, and the chemical reactions that lead to clays. The professor, John J. Renton, has the glasses, moustache, and plain demeanor you would want from a geologist, though he actually started as a chemist.
All my the last part of my life is going to be devoted to is filling the gaps left by the first part.