Salon Kitty
Salon Kitty was a Berlin brothel used by the SD for espionage purposes before and during World War II.
http://en.wikipedia.org/wiki/Salon_Kitty
The idea to use Salon Kitty for espionage purposes came from Reinhard Heydrich, but SD chief Walter Schellenberg did most of the work.
One of the customers was Count Galeazzo Ciano, Foreign Minister of Italy, whose forthright opinions about the Führer were not particularly positive. Another one, SS commander Sepp Dietrich, wanted all the 20 girls for an all-night orgy but he dropped no secrets. Additionally, Goebbels had been marked as a client by some. He, apparently, enjoyed the 'lesbian displays' that were otherwise considered anti-social acts outside of that context.
However, British agent Roger Wilson, under his cover identity of Romanian press secretary Ljubo Kolchev, noticed when the wires were rerouted to another listening position. He became a regular customer of Salon Kitty, with a regular girl, and later arranged a wiretap to three cables. Now British intelligence heard some of the same conversations SD did. Wilson was later captured and sent to a POW camp.
In 1976, these events were turned into the highly controversial film Salon Kitty, directed by Tinto Brass and starring Helmut Berger as Walter Schellenberg (re-named Helmut Wallenberg) and Ingrid Thulin as Kitty Schmidt (re-named Kitty Kellermann.)