When he was little, this was one of my son's favorite books. It tells the story of a child riding the Metrorail subway system in Washington, D.C., which he always loved to do, too. It is beautifully written, with brief but vivid descriptions of what it's like to ride on the underground train, and of what is happening above the train tunnel. It's a great read-aloud book, with the cadence of the words reflecting the speed of the train. In fact, I read it aloud today at a bookstore's story time, and the preschoolers loved seeing and hearing about the trains and the places they know.