We present a new method that uses a generative adversarial network to learn how to locally redistribute the mass in lognormal mass maps to achieve N-body quality full-sky weak lensing maps. Our mass maps reproduce a broad range of weak lensing summary statistics with percent level accuracy. Producing a single full-sky map requires ~10 seconds on an average compute node with no GPU acceleration. Relative to running a dark matter simulation, our algorithm reduces run time by more than four orders of magnitude.