What’s the best non-fiction book you’ve ever read that isn’t self-help books?

I'm trying to expand my reading list and want to discover some truly remarkable non-fiction. Not looking for self-help books or motivational guides—I'm interested in books that taught you something profound, changed the way you think, or just blew your mind with ideas, history, science, or philosophy.

What’s the best non-fiction book you’ve ever read that isn’t self-help, and why did it leave such an impression on you?