Railsea is a "big idea" book. This is not unusual for China Miéville. This book does the same thing for trains that Embassytown
does for language. It expands the idea of rail-traveling trains in new directions, stretching our understanding while remaining faithful to their basic nature. The author has covered some of this ground before. In Iron Council
he showed what might happen when a train's crew strikes out on their own, removing the tracks behind them and building a new route ahead. Railsea takes things a bit further.
Readers explore a world in which, unsurprisingly, train tracks cover most of the surface much like our ocean covers everything below... well, sea level. Some rocky islands are free of rails and of the poisoned soil beneath them. On these islands are the world's ports and cities. A variety of trains traverse the sea of rails. Some perform tasks similar to our familiar ocean-going ships: trade, exploration, "naval" military engagement, and even piracy. Others have stranger missions. There are trains that hunt the dangerous animals that burrow rapidly though the toxic soil. And there are the mysterious Angels that repair the rails for reasons of their own.
The railsea itself is such a well-crafted integration of the familiar and fantastic that it easily steals the reader's attention from the book's human characters. The characters' actions are interesting, but seem incidental compared to the continuing flow of new information about the railsea. It is enough to know that a young doctor's apprentice on a train that hunts giant moles finds pictures taken by a lost expedition. Soon joined by others, he follows this expedition's trail toward something new, interesting, and perhaps financially rewarding on the furthest shores of the railsea. You will have to join them to learn what they find.
I recommend this book highly. It is entertaining, imaginative and engaging. China Miéville's skills as a writer and storyteller have enabled him to create a reading experience well worth your time and attention. Enjoy!