It was then that my viewpoint changed. I envisaged, very suddenly, that our aëro was flying overturned. This land was beneath us, not above! Hanging head downward, as I have often done in a Wasp, I was staring down at this dark surface over which we were speeding. And as though to verify the fancy, I heard Entt speak, and saw him swing us. The void began slowly turning over. The dim stars came slowly swinging overhead; the rocky ceiling went down and steadied horizontally beneath us. Normality came again. I grasped it now. This void, this titanic cave, was peopled on all its inner surface. Floor and ceiling, no difference. So strange! And yet was it? My fancy held that just a moment ago, this void had swung completely over. Our whole great earth lying outside it, had turned. This ceiling, which now was beneath us, was not a ceiling, but a floor. But in reality it was only our aëro which had turned. So strange a thing, this inner surface peopled both top and bottom; up and down. But was it so strange? On the surface of our earth, we in the Americas visualize ourselves always as upright. Our heads are to the stars; our feet to the great earth which always lies bulging under us. And we can fancy China, down there with all its people hanging head downward. Yet we know that in twelve hours, they must be on top, and ourselves hanging down. Up and down! Meaningless terms when used to try and denote anything of the Absolute! There is, indeed, in all our universe, no term of time or space, or motion that means anything, when taken by itself alone. The gravity here in this void? The new textbooks explain it in most learned fashion. They talk of different air quality, different pressure down here. The great bulk of our earth, encompassing this inner void to give rise to whole new sets of mathematical formulæ. They say that our scientists had never before encountered an underground area which had its own atmosphere, subject to its own pressures and laws. Let them have their say; I tell only what I saw and felt. We were dropping suddenly downward in a swift spiral. Arturo touched me. “The City of the Mound. See it there?” A low, rocky mound-shaped hill lay beneath us, a mile or so off to one side. It was dotted with lights, covered with houses--low, circular houses, seemingly of a gray-black stone. We dropped lower. The mound was perhaps three hundred feet high. The houses were set on its slopes, in tiers. Streets were between them, in orderly array--horizontal streets, like circular bands around the hill; and there were other streets running down the slope. One side was a gentle declivity; the other, a steep, almost precipitous descent. The street there went down a broad, metallic ladder. Arturo gestured. “Her house is there--the Great Woman. At the top of the mound.” The wind was lessening as our flight slowed and we settled. I demanded: “What woman? That one we saw in the tenth lock?”