Down the dim-lit corridor we ran, past open doors in its walls through which we glimpsed great halls and branching passageways, all seeming for the moment deserted. A few moments later we had reached the corridor's end, and were peering out into the gigantic, white-lit space that lay beyond, a space alive and clamorous with the same multifarious activity as when we had come through it. To venture out into that great place of humming machines and thronging nebula-creatures was to court instant death, we knew, yet it must be crossed to gain the single shaft that led upward. Then, while we still hesitated, I uttered a whispered exclamation and pointed to something in the shadows beside us, something big and round that lay just inside the broad corridor's dusk, and that gleamed faintly in the dim light. In a moment we were beside it, and found it to be one of the great turtle-machines that swarmed across the floors of the vast caverns beyond us, though this one was unoccupied, its round door open to expose the hollow interior of the dome. "There's our way out!" I cried. "There's room in it for the three of us!" Within another moment we were inside it, crouching together in the cramped space of the interior and swinging shut the little door. I found that a narrow slit running around the dome allowed us to look forth, and that a little circle of switches grouped around a single large lever were evidently its controls. Swiftly I pressed these switches in a series of combinations, and then there came a welcome hum of power from beneath and we were gliding smoothly out of the shadowy corridor into the full glare of the thronging, white-lit cavern, my hand on the central lever guiding our progress. Tensely we crouched in our humming vehicle as it moved smoothly across the cavern, between the rows of great machines, toward the corridor opening in the opposite wall. The thronging nebula-creatures about us paid us no attention whatever, taking us for but one of the scores of turtle-machines that were busy about us. Hearts beating high with our success we glided on toward the dark wall-opening that was our goal. A score of feet from it we suddenly held our breath as another of the turtle-machines collided suddenly with our own, but in a moment it had glided away and in another moment we were again in the shadows of a dim-lit corridor, gliding down its length toward the shaft that led upward.