"Well, if we strike away from here, we'll just get right back in again." Shann waved a hand toward the mist, waiting as if with a hunter's watch upon them. "And we certainly can't go down." He dug a boot toe into the sand to demonstrate the folly of that. "So, what about up?" He ducked under the spinning disk to lay his hands against the surface of the giant slab. And in so doing he made a discovery, revealed to his touch although hidden from sight. For his fingers, running aimlessly across the cold, slightly uneven surface of the stone, slipped into a hollow, quite a deep hollow. Excited, half fearing that his sudden guess might be wrong, Shann slid his hand higher in line with that hollow, to discover a second. The first had been level with his chest, the second perhaps eighteen inches or so above. He jumped, to draw his fingers down the rock, with damage to his nails but getting his proof. There _was_ a third niche, deep enough to hold more than just the toe of a boot, and a fourth above that.... "We've a ladder of sorts here," he reported. Without waiting for any answer from Thorvald, Shann began to climb. The holds were so well matched in shape and size that he was sure they could not be natural; they had been bored there for use--the use to which he was now putting them--a ladder to the top of the slab. Though what he might find there was beyond his power to imagine. The disk did not rise. Shann passed that core of light, climbing above it into the greater gloom. But the holes did not fail him; each was waiting in a direct line with its companion. And to an active man the scramble was not difficult. He reached the summit, glanced around, and made a quick grab for a secure handhold. Waiting for him was no level platform such as he had confidently expected to find. The surface up which he had just made his way fly-fashion was the outer wall of a well or chimney. He looked down now into a pit where black nothingness began within a yard of the top, for the radiance of the mist did not penetrate far into that descent. Shann fought an attack of giddiness. It would be very easy to lose control, to tumble over and be swallowed up in what might well be a bottomless chasm. And what was the purpose of this well? Was it a trap to entice a prisoner into an unwary climb and then let gravity drag him over? The whole setup was meaningless. Perhaps meaningless only to him, Shann conceded, with a flash of level thinking. The situation could be quite different as far as the natives were concerned. This structure did have a reason, or it would never have been erected in the first place. "What's the matter?" Thorvald's voice was rough with impatience. "This thing's a well." Shann edged about a fraction to call back. "The inside is open and--as far as I can tell--goes clear to the planet's core." "Ladder on the inside too?"