I can't believe peoples outright refusal to even contemplate that the Earth may be flat rather than round, you always get that old chest nut 'But why don't boats etc fall off the edge?'. Its simple really, it's the same reason that people in Australia and Argentina don't fall off this so-called spherical planet, that is to say Gravity.
Is it so hard to believe that when you reach the 'Edge of the planet, you simply flip over to the other side and continue your voyage without ever knowing what just happened?, I believe not.
My theory on the fact that no-one has seen the actual edge boils down to light inversion, rather like a desert mirage, where the air gets heated at the edges of the earth, and the hot air above the rim reflects the other side, so that anyone traveling towards it, would not see any change in terrain.