We investigate the high- and low-frequency magnetotransport of a square antidot lattice with a triangular basis. In the longitudinal magnetoresistance ρxx(B) we observe higher-order commensurability features which reflect skipping orbits along the straight edges of the antidots. A magnetic field asymmetry in the four-probe resistance along the y-direction allows us to test basic symmetry relations in the transport coefficients. Under far-infrared irradiation the broken symmetry of the antidot array leads to a lateral photo-voltage which is attributed to a lateral, ratchet-type mechanism.