I started this thread because I find that books of photos of particular types of places often help me describe things I am trying to imagine but feeling some difficulty getting the vision to come clear. Since my writing is mostly fantasy, I like to use books with landscapes and urban environments too. Please add yours!
These are books I like because browsing through them can help me create a specific type of place in my mind. It helps sharpen the inner eye of vision, and can help you describe a place you have already invented (or... a place you are writing about or referencing but can't visualise or have forgotten).
Sacred Earth: Places of Peace and Power by Martin Gray (9781402747373) Lots of fantastic pictures, landscapes and descriptions.