San Francisco is standing on the brink of disaster - it sits on one of the world's most infamous earthquake hotspots – the San Andreas Fault. How do the city's buildings and infrastructure survive the onslaught of a destructive earthquake? This film looks beneath the city's skin to discover the engineering wonders and geological forces that make it possible. Stunning CGI animation peels back the glass of its skyscrapers and steel off its bridges to reveal their inner workings. The engineers and geologists who know this city the best reveal the secrets inside San Francisco's skyscrapers that keep them standing, protect them from raging fires and keep residents safe during the deadliest quakes. The film explores the geology that shaped the city's past and challenges its future, from the valleys that hold the city's fire-fighting water to the fault line that is overdue for a massive earthquake.

Sydney is a city bursting at the seams – home to a fifth of 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.

Beneath the streets of London, lies a parallel universe. As its buildings soar higher, so its tunnels go deeper. London has more infrastructures built underground than any city in the world. They hold the key the city’s success. This episode strips away the ground to reveal the city's inner workings and explores the ingenious technologies that helped engineers to build one of the biggest cities on Earth. We join engineers working in this vast underground city – from tunnel builders digging a brand new underground train line 40m beneath the city to squads of workers scrubbing its sewer tunnels to prevent outbreaks of disease. We lift up Buckingham Palace to reveal a "lost" river and show the innovative engineering behind the city’s brand new port under construction. We peel away the Tower of London to reveal the true scale of the river Thames – far from being quiet and obedient, it was once a tidal torrent. And we strip back the steel and glass from Europe's tallest skyscraper - the Shard – to reveal its hidden inner workings. This episode explores the geology that shaped the city's past and challenges its future, from the rich clay that it sits on to the river that may one day consume it.

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.

Dubai is a gleaming metropolis, grown from the desert sands in just a few decades - yet it sits in one of the driest places on Earth, is pummelled by raging sandstorms, and its skyscrapers are resting on top of sand. This episode looks beneath the city's skin to discover what keeps Dubai's buildings standing, protects them from desert storms, and keeps residents alive in the searing heat.

Ancient Rome is the prototype of all modern cities. 2,000 years ago it was the biggest in the world - home to a million people. It has survived better than any ancient city on earth and today is home to 3 million citizens. How did Rome become the "Eternal City?" This film strips its most famous icons bare to reveal their secret inner workings and the ingenious technology that allowed engineers to build the Pantheon, Coliseum, Trevi Fountain and Via Appia. Roman engineers' mastery of constructing buildings, roads and viaducts set the city on course to become the greatest Empire the world had ever seen. By exploring deep underground we reveal the crucial role volcanoes played in the city’s growth. We descend into a cavern of tunnels that runs under most of Rome, abseil into an ancient aqueduct and explore how Rome's new Metro is being built. This film explores the volcanic geology that shaped the city's past and challenges its future, from the ash that is a key ingredient of concrete to the lava flows that underpin its roads.