Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. An underground city (also underground mall, underground passageway, depending on size, shape, etc) is a network of tunnels that connect buildings beneath street level. These may include office blocks, shopping malls, train and metro stations, theatres, and other attractions. An underground city can usually be accessed through the public space of any of the buildings connecting to it, and sometimes has separate entries as well. Underground cities are especially important in cities with cold climates, as they permit the downtown core to be comfortably accessible year round without regard to the weather.