The divided city of Berlin wasa hotbed of spying activity throughout the Cold War, with one famous operation involving atunnel being built by the British and US into Communist East Berlin to enablecommunications cables to be tapped.
Russia's KGB knew about the tunnel thanks to the treachery of George Blake, but did not take action against it in order to protect their mole in British intelligence.
In the 1950s, the US National Security Agency (NSA) used Berlin's highest hill, the Teufelsberg, as a listening station.
The site was frequently used by American soldiers and its five large satellite domes on top of the building, though unused, can still be seen today.
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