The natural passageway was untenanted. Evidently its coolness and dryness made it untenable for most of Inra's humidity and heat loving life. Yet the floor was so smooth that it must have been artificially leveled. Faint illumination was provided by the rocks themselves. They appeared to be covered by some microscopic phosphorescent vegetation.
After hundreds of twists and turns and interminable straight galleries the cleft turned more sharply upward, and they had a period of stiff climbing. They must have gone several miles and climbed at least 20,000 feet. The air became noticeably thin, which only exhilarated Gunga, but slowed the Earth man down. But at last they came to the end of the cleft. They could go no further, but above them, at least 500 feet higher, they saw a round patch of sky, miraculously bright blue sky!
"A pipe!" Forepaugh cried.
He had often heard of these mysterious, almost fabulous structures sometimes reported by passing travelers. Straight and true, smooth as glass and apparently immune to the elements, they had been occasionally seen standing on the very tops of the highest mountains—seen for a few moments only before they were hidden again by the clouds. Were they observatories of some ancient race, placed thus to pierce the mysteries of outer space? They would find out.
he inside of the pipe had zigzagging rings of metal, conveniently spaced for easy climbing. With Gunga leading, they soon reached the top. But not quite.
"Eh?" said Forepaugh.
"Uh?" said Gunga.
There had not been a sound, but a distinct, definite command had registered on their minds.