Where Tarzan stood it was dark as Erebus. Not even his trained eyes could penetrate the utter blackness. Cautiously he moved forward until his out-stretched hand touched a wall, then very slowly he traveled around the four walls of the chamber.

Apparently it was about twenty feet square. The floor was of concrete, the walls of the dry masonry that marked the method of construction above ground. Small pieces of granite of various sizes were ingeniously laid together without mortar to construct these ancient foundations.

The first time around the walls Tarzan thought he detected a strange phenomenon for a room with no windows but a single door. Again he crept carefully around close to the wall. No, he could not be mistaken! He paused before the center of the wall opposite the door. For a moment he stood quite motionless, then he moved a few feet to one side. Again he returned, only to move a few feet to the other side.

Once more he made the entire circuit of the room, feeling carefully every foot of the walls. Finally he stopped again before the particular section that had aroused his curiosity. There was no doubt of it! A distinct draft of fresh air was blowing into the chamber through the intersection of the masonry at that particular point—and nowhere else.

Tarzan tested several pieces of the granite which made up the wall at this spot, and finally was rewarded by finding one which lifted out readily. It was about ten inches wide, with a face some three by six inches showing within the chamber. One by one the ape-man lifted out similarly shaped stones. The wall at this point was constructed entirely, it seemed, of these almost perfect slabs. In a short time he had removed some dozen, when he reached in to test the next layer of masonry. To his surprise, he felt nothing behind the masonry he had removed as far as his long arm could reach.

It was a matter of but a few minutes to remove enough of the wall to permit his body to pass through the aperture. Directly ahead of him he thought he discerned a faint glow—scarcely more than a less impenetrable darkness. Cautiously he moved forward on hands and knees, until at about fifteen feet, or the average thickness of the foundation walls, the floor ended abruptly in a sudden drop. As far out as he could reach he felt nothing, nor could he find the bottom of the black abyss that yawned before him, though, clinging to the edge of the floor, he lowered his body into the darkness to its full length.

Finally it occurred to him to look up, and there above him he saw through a round opening a tiny circular patch of starry sky. Feeling up along the sides of the shaft as far as he could reach, the ape-man discovered that so much of the wall as he could feel converged toward the center of the shaft as it rose. This fact precluded possibility of escape in that direction.

As he sat speculating on the nature and uses of this strange passage and its terminal shaft, the moon topped the opening above, letting a flood of soft, silvery light into the shadowy place. Instantly the nature of the shaft became apparent to Tarzan, for far below him he saw the shimmering surface of water. He had come upon an ancient well—but what was the purpose of the connection between the well and the dungeon in which he had been hidden?

As the moon crossed the opening of the shaft its light flooded the whole interior, and then Tarzan saw directly across from him another opening in the opposite wall. He wondered if this might not be the mouth of a passage leading to possible escape. It would be worth investigating, at least, and this he determined to do.

Quickly returning to the wall he had demolished to explore what lay beyond it, he carried the stones into the passageway and replaced them from that side. The deep deposit of dust which he had noticed upon the blocks as he had first removed them from the wall had convinced him that even if the present occupants of the ancient pile had knowledge of this hidden passage they had made no use of it for perhaps generations.