As they passed through the stone door, Tom and Professor Bumper tried to get some idea of the mechanism by which it worked.  But they found this impossible, it being hidden within the stone itself or in the adjoining walls.  But, in order that it might not close of itself and entomb them, the portal was blocked open with stones found in the passage.

“It’s always well to have a line of retreat open,” said Tom.  “There’s no telling what may lie beyond us.”

For a time there seemed to be nothing more than the same passage along which they had come.  Then the passage suddenly widened, like the large end of a square funnel.  Upward and outward the stone walls swept, and they saw dimly before them, in the light of their torches, a vast cavern, seemingly formed by the falling in of mountains, which, in toppling over, had met overhead in a sort of rough arch, thus protecting, in a great measure, that which lay beneath them.

Goosal, who had brought with him some of the fiber bark torches, set a bundle of them aflame.  As they flared up, a wondrous sight was revealed to Tom Swift and his friends.

Stretching out before them, as though they stood at the end of an elevated street and gazed down on it, was a city—­a large city, with streets, houses, open squares, temples, statues, fountains, dry for centuries—­a buried and forgotten city—­ a city in ruins—­a city of the dead, now dry as dust, but still a city, or, rather, the strangely preserved remains of one.

“Look!” whispered Tom.  A louder voice just then, would have seemed a sacrilege.  “Look!”

“Is it what we are looking for?” asked Ned in a low voice.

“I believe it is,” replied the professor.  “It is the lost city of Kurzon, or one just like it.  And now if we can find the idol of gold our search will be ended—­at least the major part of it.”

“Where did you expect to find the idol?” asked Tom.

“It should be in the main temple.  Come, we will walk in the ancient streets—­streets where no feet but ours have trod in many centuries.  Come!”

In eager silence they pressed on through this newly discovered wonderland.  For it was a wonderful city, or had been.  Though much of it was in ruins, probably caused by an earthquake or an eruption from a volcano, the central portion, covered as it was by the overtoppling mountains that formed the arching roof, was well preserved.

There were rude but beautiful stone buildings.  There were archways; temples; public squares; and images, not at all beautiful, for they seemed to be of man-monsters—­doubtless ancient gods.  There were smoothly paved streets; wondrously carved fountains, some in ruins, all now as dry as bone, but which must have been places of beauty where youths and maidens gathered in the ancient days.

Of the ancient population there was not a trace left.  Tom and his friends penetrated some of the houses, but not so much as a bone or a heap of mouldering dust showed where the remains of the people were.  Either they had fled at the approaching doom of the city and were buried elsewhere, or some strange fire or other force of nature had consumed and obliterated them.