The Plutonian refuge had not been built to offset attack from the surface of the planet itself. It was no thick rampart of unbroken plastic as the walls of the other Sun-tap stations had been. Close up, it proved to have many doorless entryways, ramps running up to higher floors, even wiry monorail scaffolding, probably left behind by the builders.
They entered an opening in the base. Once inside, dim lights set in the ceiling lighted the path before them. They walked down this culvert like rats in a giant sewer until they came to a wall studded with several doors.
The doors were shut, but a tiny globe set on the surface of each one reacted to Burl's charged touch. Two opened upon dark airless passages. The third resisted a moment, and when it did open, there was a whoosh of air which raised a momentary cloud of dust on the stone floor of the culvert. This was obviously the entrance to the inhabited portion of the refuge.
The men closed the door behind them. They were in a small chamber. A door on the other side was opening automatically. "An air lock system," muttered Russ as they went through.
They were now inside the vast building itself. There was air, and, after testing it, they opened their helmets. The air was almost as thick as that of Earth, and they experienced no difficulty in breathing. It was stale and somewhat metallic in flavor, probably because it had been enclosed and used over and over for thousands of years.
They saw no living beings, which seemed strange. "Apparently these people really are at their last gasp," remarked Russ as they passed through an area that had obviously once been a large dormitory. They heard distant humming sounds somewhere in the floors above, but all that was visible on the lower level seemed to be maintenance machinery.
They walked through great storerooms which were piled high with sealed drums. They saw factories lying silent—curious lofts of odd machines powered by globes that were idle. They skirted an unlighted reservoir of water in a circular chamber far in the interior. And here and there in the gloom, they spotted huge ramps leading spirally upward.
Finally they turned their steps up a sloping ramp, mounting one floor and then another, and another. They were tired, but curiously exhilarated. They felt that they were about to strike at the heart of the foe, and that his days were numbered at last.
They emerged on a higher level, lighted more brightly than the others. Here they saw globes that glowed with the same intensity as those in the Sun-tap stations had. They moved carefully now, keeping out of sight, and several times they saw shadows in the distance or heard the thump of something moving.
They worked their way by instinct to what they guessed was the center of operations. They peered, at last, through a low, wide doorway into a large chamber. Here was a mass of mighty globes and rods, some revolving as they circled the metal masts that came through the room from the ceiling above.