Are they delivered by a stork carrying a small pink or blue blanket in its beak? Do you find them in the cabbage patch, or do they spring fully formed from the mind of the author?
If your answer is "none of the above", books spring from ideas, hard work and imagination then read on.
I am often asked where the inspiration comes from for my books and stories. I rarely answer this question directly when this is put to me for the sources are so varied, A piece I have read in the paper, a book by another author, a colour, a scent, a magazine article, it can be anything.
I suppose I take inspiration from many things though I have rarely bothered with writing prompts.Often an authors way of planning a book. Other's books do inspire me but that is often because of the writing style or ideas contained therein rather than the content. Landmarks, landscapes and ruins(etc) particularly inspire me. How did the people that lived here survive? how did they build it?, Why was it built? and so on.
Once upon a time I visited a stone circle in Kilmartin Glen (Scotland), I found it magical, the name alone conjured up ideas (The Lady Glassery forest) and then finding that the stones had stood for thousands of years before the pyramids, I wondered what gods the people of the time worshiped, how they survived and so on and that led to research; a motivator in in itself.
I do not think it really matters where your writing inspiration comes from, rather it is, simply that you recognize the motivation for what it is when you have it and then write it down. Hopefully translating those thoughts and ideas into a good book or story.
I like to think that I can lay claim to that accolade from time to time.