I read a great deal of history. For me, it is the touchstone for most of my fiction. I'll mention this often and probably repeat myself as I line out some of the things that have inspired me. Some little piece of the real world's past will work into my brain and twist and turn until I have an idea of my own. One of my favorite biographies is Disraeli: Portrait of the Victorian Age by Andre Maurois (translated by Hamish Miles -- other translations are not as good). As soon as I had finished reading the book the first time, I knew that I wanted to write about someone like Disraeli, at least in one aspect: I wanted someone who rose to power but who should never have had such a chance.
So I wrote Silky about a young slave who makes a choice to help someone else and changes his life. It is probably my most popular book.
Almost all the nonfiction books I read are filled with little flags that mark some line or another.
Their Babylonian neighbors, in fact, regarded Elam as especially the land of witches and of demonic creatures.... -- Cambridge Ancient History Volume II, Part 2 The Middle East and the Aegean Region c. 1380 to 1000 BC
That little bit gave me a wonderful piece of background for Beware the Wrath of Bunny Hopper.
And then there are the things that I would love to use but are far too much tied to the real world and would be recognized. Take, for instance, an amusing incident at the time Alexander was crossing the Gedrosian Desert. This was actually something that happened with the fleet, under Nearchus, which was supposed to sail along the shore and provide support. The Monsoons (which the Macedonians didn't understand at all) held the fleet up at the Indus delta. Eventually, Nearchus sailed, though several months after Alexander had taken part of his people into the horrible, inhospitable country.
Somewhere out in the ocean, the fleet spotted a pod of whales.
Whales are not found in the Mediterranean Sea. The largest sea creature the Greeks and Macedonians had dealt with before this was probably the friendly porpoise. Now they found this group of monsters breaching and pounding into the water. Nearchus decided there was only one thing to be done. He had his ships -- about 30 triremes -- line up and ... they charged the whales.
The whales must have been amused. They dived down, swam under the ships and up again on the far side. Nearchus called it a win. Ships and whales sailed away.
Who knows? Someday I may find a way to work at least the absurd aspects of this encounter into a story. It's just too good to ignore.
Ideas can come from anywhere but I do enjoy going out in search of them. Learning more about the world opens up new worlds of fiction for me. I'll never be able to write all the ideas, but that's not going to stop me from the joy of finding more of them. There are just far too many fun ideas out there.