Speed. Color. Sound. Numbers. Maps. Connections. Navigation. Subway systems may be specific to certain cities around the world, but the pure thrill of a subway ride is universal to all young children. Christoph Niemann’s graphically elegant and playful picture book is a tour de force for preschoolers and a stellar addition to the canon of books about trains, trucks, planes, and automobiles. Based on the author’s own underground adventures with his young boys—chronicled for adult readers in Niemann’s New York Times blog, Abstract City—this innovative picture book is an invitation down underground, where a system of trains and tracks delivers millions of riders to their destinations each day. “Underneath the city is this beautifully simple system of letters, numbers, and colors. The trains and stations are huge and impressive but also comforting, because nothing ever changes. My boys are in charge; they can read the signs, navigate the grid, and they always know what happens next.”—Christoph Niemann