This main abyss, through which we had flown, was lens-shaped--some forty or fifty miles between the surfaces at its greatest diameter, and in length perhaps three hundred miles. He thought that it lay, not as I had visualized, flat beneath the floor of our Pacific Ocean, but tilted diagonally edgewise. We had entered near its upper end, where it reached within a few miles of the ocean bed. We had flown down its length. The City of the Mound, then, must lie two hundred miles or more underground. There was, at the upper end, no exit except the system of locks down which we had come. “There’s no escape that way, Jeff. The Gians have a few hundred of those sub-sea vehicles. A few are large ones--as large as the locks will take. The locks were built, a generation ago, for this purpose. The Gians have been planning this thing for that long. Rhana is about ready now. Her army--and all the Gians--will escape upward that way.” “How many of them are there?” “Not many. I suppose forty or fifty thousand. They’re all here in the City of the Mound, and in two other cities across on the other surface. They’ll be starting soon. But what about the Middge? A million of them, I imagine. They can’t get through the locks. No vehicles to spare--no room, no time.” From this main lens-shaped abyss, caverns, tunnels and passageways everywhere opened off, especially at this lower end. It was a vast honeycomb. Tunnels led to caverns and pits glowing with molten fire. There were vast passages, black and unexplored; no one could guess where they led, in this vast honeycomb, the sub-surface shell of our earth--the porous, thick skin of an orange. There was, near the City of the Mound, a passage a mile or two in width. It plunged steeply downward. Erroneous term! Who could say, downward, or upward? It led, within a few hours on foot, to another great abyss. A black oily sea lay on one of its surfaces. The black space facing it--floor or ceiling as you will--had never been explored. This watery abyss they called the realm of the monsters. No human lived there. Fearsome monsters of the deep, and flying things, and things that crawled, were there. Sometimes they would wander through the tunnel passage out into the abyss here where humans had their cities. The passage now was always guarded with flood lights. The monsters feared the light; its faintest glow blinded them; it turned them back. For generations now none of them had come through. I said, “These people seem very advanced with their science, Arturo. Engineering achievements--why didn’t they wall up this connecting passage completely? You say it’s only a mile or two wide.” * * * * *