If you're interested in the history of how the Poles and then British not only cracked the German Enigma Cipher machine used in world war 2, but then operationalized the interception, decryption and dissemination process - this is the place. There's quite a bit written about how the Enigma cipher system worked, but it isn't until you get to Bletchley Park do you understand the size, scope and scale of how they turned decryption of intercepted messages into an industrial process that gave the Allies a strategic edge in WW2. A must visit next time you're in London (35 minute train from Euston station, 5 minute walk to the museum.)