After a time he reached a circle of pillars grouped like the monoliths of Stonehenge, with a large carved altar on a base of three steps in the center; and so curious were the carvings on that altar that he approached to study them with his electric light. But when he saw what they were he shrank away shuddering, and did not stop to investigate the dark stains which discolored the upper surface and had spread down the sides in occasional thin lines. Instead, he found the distant wall and traced it as it swept around in a gigantic circle perforated by occasional black doorways and indented by a myriad of shallow cells with iron gratings and wrist and ankle bonds on chains fastened to the stone of the concave rear masonry. These cells were empty, but still the horrible odor and the dismal moaning continued, more insistent now than ever, and seemingly varied at times by a sort of slippery thumping.