The City & the City by China Mieville is unique as it is challenging and difficult to read (listen). This book forces 
readers to understand all the nuances of the altered reality that Mieville creates. A solid understanding of this altered world is not obtained until you are well into the book
In a small corner of Europe, the cities of Beszel and Ul Quoma exist uneasily side by side but overlapping. These cities are divided by language, culture, and their perceptions of reality. Inspector Tyador Borlu, the main protagonist, of the Beszel police Extreme Crime Squad confronts his most vexing criminal case, the murder of young American archaeology graduate student Mahalia Geary. Initially it appears to be a routine homicide, but it turns out not to be the case. Borlu is thrust into complex conspiracies that threaten to shatter the uneasy coexistence of these two cities.
If you like reading books that are different and challenging, then this is surely a book for you.