Initially ridiculed, underground railways are now a success around the world. The era of underground passenger transport began more than 150 years ago in London with steam locomotives. The smoke was even “sold” as a cure by the operators. The tunnel network was gradually expanded using the shield tunnelling method and electric trains replaced the steam locomotives. Great Inventions ventures underground around the world, watches giant drills cut their way through the earth and takes a look into the future of the subway.