[math-fun] Locally isometric polyhedral embedding of flat torus

Where can I learn about, and see pictures of, polyhedral surfaces in R^3 that are locally flat (the angles at each vertex add up to 360 degrees) and have the global topology of R^2/Z^2? More specifically and concretely, how can I crease and fold a square sheet of paper [0,1]x[0,1] so that I can actually glue (t,0) to (t,1) and (0,t) to (1,t) for every t in [0,1]? Jim Propp