They agreed to pay him in advance, and soon they set out from the hotel in Pera, eager to see the mysterious place that was said to hold so much of mystery and danger. In the afternoon sunshine Stamboul was magnificent when seen from a distance. But when they had crossed the Golden Horn and plunged into the city all its impressiveness vanished. At intervals they came upon some splendid mosques, but mosques were far more impressive when seen from the proper distance. Mustapha knew his business, and he conducted them to the place where they could descend and inspect the Underground Palace, but he declined to enter with them. For that purpose he called another man, with close-set, shifty eyes and a thin-lipped mouth. “This dragoman, Bayazid,” he said. “He tak’ you.” “Is he trustworthy?” asked the professor, with a slight show of nervousness. “You not find one more so, effendi.” So Bayazid, or “Pigeon,” as he was called in English, was engaged to show them the Underground Palace. “I haf very good boat, effendi,” he declared. “Whatever is that?” asked Buckhart. “Do we have to take a boat?” “You will see,” answered Zenas. The entrance was somewhat like that of a sewer, but there were stone steps leading down into the darkness of the place. The guide found and lighted two torches, which it seemed were kept for the use of those who wished to visit the Palace. “Say, this is some boogerish!” said Brad, as they found themselves in a dark and damp cemented passage. “The old city was built above a huge system of cisterns,” explained the professor. “Their purpose was to guard against a famine of water in time of war. Some of the old cisterns are dry now and are used by silk spinners. We shall visit one that still contains water.” “But I thought we were going to see a palace,” said Dick, in disappointment. “You shall see one—so called.” The passage echoed to their tread, while their voices came back hollowly, as if hidden imps were mocking them. But the boys were quite unprepared for the spectacle that suddenly met their gaze. They came from the passage into a mighty vaulted chamber, stretching away into an unknown distance and filled with a shadowy maze of marble columns, row on row. The floor of this wonderful place was smooth as a mirror and seemed black as ebony, save where the light of the torches fell on it. There it glittered, and gleamed, and shimmered. Exclamations of astonishment and wonder broke from the lips of the two lads. The professor grasped them, one with either hand, and stopped them abruptly. “We can’t go farther on foot,” he said. “Eh? Why not?” asked the Texan, in surprise. “Look at that floor! Wouldn’t it be great to dance on! It’s smooth as glass and——” “You would get your feet wet if you attempted to dance on that,” declared Zenas. “What? Why—why, it’s water!” “Exactly.” “But—but it looks black everywhere except where the light strikes directly on it.” “Because no other ray of light reaches this place.”