Invisible Cities is a short novel about the fictitious adventures of Marco Polo. Polo is in conversation with the emperor Kublai Khan and describes various cities he claims to have seen in his travels. The details of these cities form into indirect commentaries on various aspects of human existence.
The book gets your adventurous imagination running with the aesthetics of the cities, but also gives your analytical mind some of the most compelling information to attempt to piece together into a meaning. You may never fully unravel what each city means (I know I haven't), but just trying is a very insightful and enlightening experience. Since the book is short and extremely dense it lends itself well to re-reading, each time you read it reveals even more meaning you didn't know was there.
I highly recommend this book, it is challenging but very much worth the effort. It's so challenging that I don't feel qualified to write a thorough analysis in the spoiler section yet, so I will end the review here.