American Gods: Author's Preferred Text
You can conjure anything based on belief, especially gods and monsters. The central conceit of American Gods by Neil Gaiman is that because humans believe in the gods, the gods exist. Fairies, kobolds, immortal queens and kings, and so forth are real simply because humans sought explanations for their world. It is an excellent idea to base a novel around and Gaiman takes readers on a tour of the spiritual landscape of the world and the backroads and quiet centers of the American continent.