Tunnel Portal

Stone tunnel portal facing -z at z = 0: a horseshoe arch with dressed voussoirs and keystone, a string course and parapet, wing walls stepping down to the sides, about 7 m tall; a tracks knob of single or double.

风格：low-poly, flat-shaded vertex colors, no textures, single shared material, so any set of these merges to one draw call; shares palette and scale with its kit