Invisible Cities is a novel by Italo Calvino.
I believe I heard of its existence through Monsters & Manuals.
I really recommend that you read it. Partly because, yes, it has some relevance to the topic of imaginary places (a central element of this hobby), but also because it is cunningly perceptive of our real world (and the image thereof we each build in our minds), and a work of art in its own right. Having read it twice, I daresay it is one of the most important books to who I am now.
Don't research it overmuch before you read it. The book is designed to open itself to you slowly. It is not long; you will not burden yourself by beginning it. It lends itself well to regular but episodic reading. A page or two before bed, perhaps.
(I am thinking of assembling my own "Appendix N," as it were, at some point. This book would definitely be on it.)