THE TREASURE VAULTS OF OPAR
room. Here she turned into one of the several corridors leading from it. In the darkness Tarzan could not see which one. For ten minutes they groped slowly along a winding passage, until at length they came to a closed door. Here he heard her fumbling with a key, and presently came the sound of a metal bolt grating against metal. The door swung in on scraping hinges, and they entered.
"You will be safe here until tomorrow night," she said.
Then she went out, and, closing the door, locked it behind her.
Where Tarzan stood it was dark as Erebus. Not even his trained eyes could penetrate the utter blackness. Cautiously he moved forward until his outstretched 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.
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