A room where every wall is a mirror. Light one lamp. Does the whole room glow?
Not this one. Penrose's 1958 room is built from two halves of an ellipse. Light from the corridor always crosses the axis between the two foci, so it can never get into the side pods. Move the lamp anywhere in the corridor and the pods stay pitch black. Put the lamp in a pod and the corridor goes dark instead.
(Ideal mirrors, point-like lamp. In 1995 Tokarsky did it with straight walls only.)
Your turn: put the lamp in the big upper hall. Any dark spots left? 👇