The Necker cube surface

We study geodesics on the Necker cube surface, $\mathbf N$, an infinite periodic Euclidean cone surface that is homeomorphic to the plane and is tiled by squares meeting three or six to a vertex. We ask: When does a geodesic on the surface close? When does a geodesic drift away periodically? We show that both questions can be answered only using knowledge about the initial direction of a geodesic. Further, there is a natural projection from $\mathbf N$ to the plane, and we show that regions related to simple closed geodesics tile the plane periodically. We also describe the full affine symmetry group of the half-translation cover and use this to study dynamical properties of the geodesic flow on $\mathbf N$. We prove results related to recurrence, ergodicity, and divergence rates.