The Secret Lives of Codebreakers: The Men and Women Who Cracked the Enigma Code at Bletchley Park
Want to know how they broke Nazi codes at Bletchley Park? There are a number of good books on the subject. Want to know what it was like to live and work there? That's harder. With the exception of Andrew Hodges's excellent Alan Turing: The Enigma (the exceedingly approximate source for The Imitation Game), biographies and social histories of Bletchley seem surprisingly sparse.
The Secret Lives of Codebreakers is a nice attempt to rectify the disparity. It's not super-deep, but it's a good overview and a quick read. It might not appeal to readers with no interest in the subject, but for the rest of us it's a lively portrait of a very particular place and time. It would be great preparation for a visit to Bletchley--an activity which I can't recommend highly enough. (We have some tips if you're interested.)