Was going through books I have in storage and ran into two that are full of weird fiction story prompts.
Myth: Myths and Legends of the World Explored by Kenneth McLeish. This has a big alphabetical list of mythical people and creatures from all around the world, with entries from paragraph to a couple pages (Zeus gets a pretty big write-up, for example). Each page or so is something new to make you wonder if anyone's written about ___ recently.
The Book of Werewolves by Sabine Baring-Gould. Originally published in 1865 (!) in London, it's a look at various legends and stories about lycanthropy, including examining the law and mental illness. The writing style is pretty modern to read.