I like word games (I do the ones in my daily paper) and Sudoku, which I play online.
You can go pretty far into ornithology, moving beyond visual bird ID to call/song ID, nest ID, bird behavior, and optimizing your yard for preferred species or natives. I noticed bluebirds in the open field across our back fence and put up a bleubird house 3 years ago. Wihtin hours it was occupied, and the happy couple raises 2-3 broods each spring/summer. I put up a mealworm feeder last year, and now the parents grab a few mealworms to eat and take some to the nest for the babies. A few weeks later I get to watch the babies fledge. All within a few feet of my kitchen window. Maybe I'll add some more bird houses in the future for the other species we attract to our yard with flowers, berries, feeders, and bird bath.
Since we moved to South Carolina, I've learned to identify a lot of new plants and critters (especailly beach critters like various crabs & fish and the many varieties of palms that grow here). I've enjoyed experimenting with what grows well in different parts of my yard--and this is my first experience gardening in sandy soil, which is more challenging than I expected.
I've also gotten more into cooking, especially expanding my repertoire of Asian dishes.
My daughter wanted me to become a notary so I could sign her marriage certificate, so that's been another research area for me. And I suppose I can make a few bucks as a notary, if it pleases me.
Most early mornings and late afternoons I sit in my recliner and smile coz I don't have to be anywhere, or do anything, or worry about much of anything. Nice life