Sydney is a city bursting at the seams – home to a fifth Australia's entire population and still growing. Trapped between the Blue Mountains and the ocean it sits on the driest inhabited continent on Earth and surrounds one the planet’s largest natural harbors. How did Sydney come to thrive in such an inhospitable place? This film looks beneath the city’s skin to discover the secret engineering wonders that make it possible and the geological forces that sculpted it. Stunning CGI animation peels back the glass off its skyscrapers and stone off the iconic opera house to reveal their inner workings. It also sucks the water up out of its harbor to explore its origins. The city's leading engineers and geologists reveal the secrets hidden inside Sydney's buildings and beneath its streets that allow the city to function, from the concealed contours of the harbor that allow super size ships to sail into the heart of the city to the underground caverns that store its water. This episode explores the geology that shaped the city's past and challenges its future, from the rich coal seams underneath to the deep gorges that channel bush fires right into the heart of the city.