This apse is unbelievably intact, making it easy to see how the walls step in gradually to create a corbeled ceiling. And notice the elliptical hole at the back of the room. During the summer solstice, the rising sun’s rays penetrate this opening from the outside of the temple and illuminate the apse’s interior. The light first appears as a crescent shape that hits the upright slab on the left. Then, as the sunbeam travels down the slab and across the floor, it becomes a full disc. Eventually it slims down to a sliver until it disappears at the base of the wall.