Franklin Heath, a UK security consultancy, offers plans for printing and assembling your own papercraft Enigma machine, approximately like the ones that Alan Turing and the Polish cryptographers and co broke at Bletchley Park. Now all we need are papercraft bombes, and a papercraft Collosus, and several thousand papercraft young women to work on code intercepts through the night...
The instructions note: "Using low-tack 'removable' sticky tape can make it easier to swap round and reuse the rotors if you want to do that, but it's not essential."
If you seriously want to explore paper computing, a good followup project is the legendary CARDiac computer.
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.