"You've been here twenty-five years and have never been able to escape?" asked Dark incredulously.
"This place isn't guarded," replied Old Beard, with a wry smile. "They don't have to guard it. All they have to guard are the supply room where the marsuits are kept and the motor pool of groundcars. This place is in the middle of the Desert of Candor, and no one can live in the Martian desert without oxygen."
They came now to one of the walls of the underground cavern, and Old Beard led them suddenly into a fissure that was well concealed from the walkways by a tangled screen of vegetation. They stumbled along a narrow passageway for a few feet, and emerged into a rude shaft, around the walls of which a roughly-chiseled and steep stairway led upward into pitch darkness. Here Old Beard halted.
"When I told you there's no way of escape here, it was not that I haven't tried many times," he said to Dark.
"This shaft leads up into the walls of the structure above—above, although it is still underground—and I have been up there often at night. It has long been my hope that I might be able to get a marsuit or a groundcar and make my escape, but they are kept locked up and always guarded, against the Jellies and the Toughs.
"I want to take you up and give you an idea of the place now, and later perhaps you will have some ideas to contribute. Happy and Shadow will stay down here until we get back."
Old Beard mounted the steep steps slowly, and Dark followed at his heels. Although the bottom of the "well" was lighted with the same dim light as that which spread throughout the entire underground area, there was no light at all higher up, and they had to feel their way carefully lest they fall off the narrow steps.
At the top, Old Beard stopped and Dark bumped sharply into him.
"I'm going to move down the space between the walls," Old Beard whispered. "Hold onto my hand and follow me. But don't say anything or make any more noise than you can help, because anyone beyond the wall may be able to hear you."
They moved ahead. The way was very narrow, very dark and very difficult, and frequently was choked with ventilator pipes or tangles of wiring. They had gone some forty or fifty feet, when Old Beard stopped.