In the immediate aftermath of the Second World War, the fault lines of the Cold War were drawn in Berlin. For the defeated Berliners, it was a confusing time, with rival ideologies playing out in the rubble of the post-war city.

In 1961, the wall dividing the city was built to stop the steady flow of migrants leaving East Berlin for West Berlin. From 1961 to 1989, thousands attempted to cross. Some succeeded, most were caught, but 190 people were killed. This episode follows their stories.

There are hundreds of miles of tunnels beneath the city. This episode goes beneath the surface to uncover the strange underworld of air raid shelters, train lines, Soviet bunkers, Allied bunkers, Nazi bunkers, escape tunnels and secret passageways.

John le Carré described Berlin as the city of perpetual espionage. There were an estimated 45,000 spies in the city in 1989 - mostly the East German STASI, spying on its own inhabitants, but also plenty of spies from the USSR, USA and rest of Europe.

Berlin is a train-lover's paradise. The great Berlin-Hamburg line once held the land speed world record. These massive railway stations are some of the largest 19th century structures to have survived the World War II bombing raids.

At the end of World War II, Berlin divided into four occupation zones that acted like a miniature version of the rest of Germany. The French, British, Americans and Soviets all put their marks on their quarters of the city with their cultural traditions influencing these sectors. Amazingly, Berlin remained under official occupation until 1990, and troops finally left in 1994.