gave the command to advance again.
IN time, they came to a chasmlike gorge across which was suspended a slender long thread of a bridge. Not far above the bridge, a considerable river emptied itself into the gorge in a mirrorlike ribbon. Kirby could not hear the torrent fall—or rather could not hear it strike any solid bottom. But from somewhere in the unlighted, unfathomed depths of the abyss rose strange bubbling and whistling sounds.
At the bridge, Naida paused and pointed to the land across the river. And as Kirby looked in the direction indicated, he beheld a rocky eminence rising for several hundred feet straight up from the expanse of a level, tree and grass covered plain. Atop of the plateau, glimmered the complex towers and turrets, the crenellated walls of a castle which, in its grey antiquity, seemed as old as the race of men.
"It is behind those walls that the caciques dwell," Naida said quickly. "It is behind the castle, in a series of separate houses, that the older members of the race dwell. We shall go and look upon them presently. But first we will force an interview with the caciques."
In silence Kirby took her hand, and, with the others following, they moved out upon the swaying, perilous causeway which hung above the chasm. After that, the trip across the plain to the foot of the plateau cliffs was quickly accomplished.
Here, however, Kirby thought they must face trouble, for he found that the great walls, of a sparkling, almost glassy smoothness, shot up to a height of at least three hundred feet, and that no path of any sort was visible.
"We're here," he said, "but how can we get up?"
BUT understanding began to dawn as Naida laughed, and produced from the pouch at the side of her gauzy dress four pliable discs of a substance which resembled rubber.
"You are very strong, are you not?" she asked.
"Yes."
"Then you will have no trouble in following us up the cliff. Our Serpent God, Quetzalcoatl, taught us how to climb long ago."
With that she handed Kirby the set of vacuum discs, and producing another for herself, moistened them in a pool of water close at hand. Then, as all of the girls followed her action, she strapped them to her hands and feet, and in a moment they had begun the ascent.
"Why," Kirby said presently, "with these things you could hang by your feet and walk on a smooth ceiling!"
Naida laughed, and they worked their way upward.
When the climb was accomplished and the discs were put away, Kirby found himself standing on the outer edge of a mediaeval paradise, of a magnificent plateau partly fortified by nature, partly by the hand of man.
"Ah!" he cried in deep admiration, then followed Naida.
The building—the castle—in the near distance, resembled a castle of Spain, save that there was greater beauty and subtlety of architecture. Turreted on all four corners, constructed of material which looked like blocks of natural glass, the fairylike structure was crowned by a gigantic tower of something which resembled obsidian. Up and up this tower soared until its gleaming black tip seemed almost to touch the glassy-radiant sky of the cavern.
No people showed themselves, and Kirby saw that the bronze-studded portals set in the front of the castle were closed.
Admiringly, he glanced at the surrounding land laid out in checkerboard patches of gardens and orchards where grew a bewildering variety of unknown fruits and blooms. Butterflies drifted past, and the air was freighted with the scent of flowers. Inside a walled enclosure, Kirby saw a good-sized plot
