Codebreaking is fun! (for a brilliant guy like Turing)

[A]t the higher levels, the cryptanalytic work was intensely enjoyable. Being paid, or otherwise rewarded, seemed almost a curiosity. It was also something of a holiday even from professional mathematics, for the kind of work required was more on the line of ingenious application of elementary ideas, rather than pushing back the frontiers of scientific knowledge. It was like a solid diet of the hard puzzles in the New Statesman, with the difference that no one knew that solutions existed. 

Andrew Hodges, Alan Turing: The Enigma, Centenary Ed. (Princeton: Princeton Univ. Press, 2012), p. 192