Perched on the shores of Lake Ontario, Toronto is a city of extremes. This sprawling metropolis was carved out by ancient glaciers. Today it is filled with a concrete jungle of towering skyscrapers. Each winter temperatures plummet to an arctic minus 40 degrees and the city is pummeled by savage snowstorms. How did this metropolis grow to become the largest city in Canada in such an extreme environment? This episode looks beneath the city's skin to discover the secret engineering wonders and geological forces that make it possible. Stunning CGI animation peels back the glass and concrete off its skyscrapers to reveal their inner workings and sucks the water up out of its lakes to explore their origins. The city's leading engineers and geologists reveal the secrets hidden inside the iconic CN Tower that keep it standing, protect Toronto's buildings from snowstorms and keep residents alive in the bone chilling cold. This film explores the geology that shaped the city's past and challenges its future, from the rich salt reserves that power its industry to the colossal falls that fuel the expanding mega-city.