The stairway was enveloped in a faint radiance which grew swiftly brighter as they descended. They were soon caught up in the brightness, the steps beneath them becoming a descending series of polished stone mirrors which reflected the more diffuse and distant brightness of the sunrise. Their shadows flickered across the brightness, sometimes elongating and becoming immense, sometimes contracting into wavering small replicas of themselves. They moved arm in arm through a kaleidoscope of shimmering curves and angles, a constantly increasing steepness keeping them constantly on guard, making them feel at times that they were descending an upright ladder teetering precariously in some unimaginable abyss of emptiness. They were almost at the bottom now and could see the shining surface of the disk which they had seen from above without being able to determine its precise configuration. It spread out from the base of the stairs in a translucent glimmering, a surface of smooth, almost glass-like texture that spiraled slightly downwards for perhaps a hundred feet and then became completely horizontal. Where it rose to a level gradient it widened out so that its faintly luminous edges graded off into shadows. There was a pylon-shaped structure at the far extremity of the sloping section. It could have been either a gateway or a small building, but Loring was almost sure that it was a building. He did not pause when he reached the bottom. He tightened his hold on Janice's waist and then released her, gesturing out across the brightness. "Walk fast, but don't run," he cautioned. "They may be watching us. That small tower could be anything: a communication control structure, a guardhouse, even a dwelling. We won't know until we get to it." He nodded and left the stone stairway, moving out across the glass-like surface of the disk without looking back. Janice kept almost abreast of him, quickening her steps but not quite running. Loring studied the structure appraisingly as he drew near to it. It was smooth-surfaced and completely featureless, a massive block of metal that rose to a height of about eighty feet. He halted directly in front of it and waited for Janice to join him before he reached out and ran his hand over a square foot of its smooth metal surface. The metal was yellowish with a burnished copper sheen to it. "What do you suppose it is?" Janice asked breathlessly. Loring shook his head. "I wish I knew. It could be a guardhouse or a signal tower or something of the sort. There's no entrance on this side, but there may be an entrance in back. It could have been erected here as a kind of sentry barrier to guard this particular part of the city. It could even be a remotely controlled robot structure, equipped with detective devices and destructive weapons." "You really think--"