The book explores imagination and the imaginable through the descriptions of cities by an explorer, Marco Polo. The book is framed as a conversation between the aging and busy emperor Kublai Khan, who constantly has merchants coming to describe the state of his expanding and vast empire, and Polo. The majority of the book consists of brief prose poems describing 55 cities, apparently narrated by Polo. Short dialogues between the two characters are interspersed every five to ten cities and are used to discuss various ideas presented by the cities on a wide range of topics including linguistics and human nature. The book is structured around an interlocking pattern of numbered sections, while the length of each section's title graphically outlines a continuously oscillating sine wave, or perhaps a city skyline. The interludes between Khan and Polo are no less poetically constructed than the cities, and form a framing device that plays with the natural complexity of language and stories.
Marco Polo and Kublai Khan do not speak the same language. When Polo is explaining the various cities, he uses objects from the city to tell the story. The implication is that each character understands the other through their own interpretation of what they are saying. They literally are not speaking the same language, which leaves many decisions for the individual reader.
The book, because of its approach to the imaginative potentialities of cities, has been used by architects and artists to visualize how cities can be, their secret folds, where the human imagination is not necessarily limited by the laws of physics or the limitations of modern urban theory. It offers an alternative approach to thinking about cities, how they are formed and how they function.