It could be the wives of King Henry, birdwatching, the distinguishing qualities of a good jigsaw puzzle vs. a bad one...the list goes on!
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Maximum Ride and Fairy Tale Reform School books. Nobody seems to have heard of them!
Mythological beings like Vampires, Werewolves, Sirens, Greek Gods, anything that isnt humans and isnt proven to be real.
Collecting interesting pebbles from places I visit. the Idea is to pave my garden with it when I have my own home. Not that obscure... but it always stumps my BF when he asks me "what do you want me to bring you" when he goes on an overseas trip.
Photographing the view out my front door. I have an unobstructed view of the Sierra Nevada Mountain range from my front porch.
Minecraft, different textures on my feet, torture, arson, murder, i could go on and on
Greek, Roman, and Norse Myth (guess where I got that from), and rollerskating. :D