A house built of single sheets, a lamp inside and a street lamp outside. A wall faces out, so from inside you see its other side, which the usual cull: 'back' throws away: walk in with the up arrow and the walls are gone. Press 1 for cull: 'none': both sides are drawn, and each is lit as the side it is, the inside by the lamp inside.
The second thing to see is what stops light: only a shadow. Light is worked out from which way a surface faces and where the lamp is, and does not know what is in between, so the far wall inside is lit by the street lamp straight through the near one. Press 2 and the street lamp casts a shadow: then it knows, and the far wall goes dark.
The arrows go round the house and in and out of it.