I'll have to read up on literary tropes as I'm having a hard time picking out which ones are being explored in some of the stories. For example, the city of "Armilla" is described as being nothing but a series of pipes topped with sinks, toilets, bathtubs, etc. To me, Marco Pollo (and Calvino) are forcing the reader to think of a mostly invisible system that is a _huge_ component of any city: plumbing.