Compiled from episodes of their show, which has gained millions of listeners over the past 10 years, the book introduces us to mysteries that most of us have never considered. Why are manhole covers round? Why do the Japanese infuse them with elaborate decorations? What do painted yellow symbols on streets tell us? Why are traffic lights red on top and green on bottom? What might we notice about the designs and support systems of buildings and bridges? Why have so-called love locks or love padlocks become a problem around the world? Why are some streets straight and others curvilinear?