“I’ll do that,” agreed Wendel, and away he went.

It was not long before he returned with the lantern. This had a powerful burner and lit up the subterranean chambers fully.

Down the second flight of steps the explorers now proceeded. A remarkable discovery was in store for them.

Down and down a winding way they went.

Soon it was seen that the walls of the passage were of natural conformation and that they were really in a cavern.

It trended downward for what seemed an interminable distance. Then suddenly a startling surprise was accorded all.

For they had emerged into a mighty, high-domed cavern chamber. Its limits could not be seen.

But it was nearly occupied with a mighty subterranean lake. The water flashed in the lantern’s glare.

“An underground sea!” cried Randall. “What a wonder!”

“And access to it by the Polar people,” mused Frank. “What was their purpose?”