He broke water in total darkness. He was outside the cavern, but exactly where he could not tell. Korree with his light organ had known and that was sufficient. Robin reached for a bank, felt a sloping wall. He grabbed it, pulled himself up in the darkness. That much was right. There was a tunnel here running steeply upward. He sniffed the air. It was strange—breathable, but strange. This part of the Moon enclosure was certainly cut off from the other sections, that was certain.
Robin let himself back into the water, swam for the cavern, and came up in it. He got hold of Cheeky, opened his pack, and extracted his homemade space helmet. He stuffed the monkey into it, closed end upward, and got into the water again. Moving swiftly under water, the terrified animal clutching the inside of the helmet, Robin transferred him to the other side, found a small level section by probing around, and deposited the helmet. He returned for the rest of his pack by this method, and finally everything was complete again in the new passage. By the light of Korree's head, he saw that they were in a narrow tunnel angling steeply upward. Robin's clothes and the pack had dried with great speed in the thin air and the low gravity. They made their way up this passage with difficulty and at last found themselves facing a lighted opening.
They emerged into a new cavern, but one quite different from those that had gone before. It was long, perhaps two or three miles long, but narrow, not more than a hundred feet or so at the widest. Looking upward, the steep perpendicular walls seemed to come together and closed up tightly about a quarter of a mile high.
A faint phosphorescence dimly lighted the new area. As they walked on, Robin became aware that there was no vegetation here, that his feet were moving through light dust. He let it run through his fingers. It felt chalky as pumice.
He looked around them again and then he realized that he had at last reached the surface of the Moon. He was walking through the bottom of a long crack in the surface, a cleft that had somehow closed up again to preserve a cache of air. But this dust, this was the surface dust of Luna, fallen to the bottom of the cleft!
As they walked, the dimness seemed to diminish. A whitish glow began to envelop them. Robin blinked at the strange light. Things began to take on strange colorations that he had not noticed before. He looked upward and saw that the ceiling of the cleft no longer was bathed in blackness. Instead there seemed a break there, a glassy glimmer through which poured a dazzling white light.
Somewhere up there the crack had been sealed by volcanic action into grayish natural glass. Somewhere outside the sun was shining down upon the Moon. Its rays were bathing the surface above the concealed cleft and some were finding their way down. For the first time in many long and difficult months Robin felt warmth and light together. He had reached the sunlight!
[13. The Sun and the Trap]
There had been a distinct chill in the strange surface canyon, but from the moment that the white sunlight began to stream in, there was a definite warming effect. The rays were diffused by the substance above which sealed the cleft, yet the sun was strong while it lasted. Robin felt good as he bathed in its rays. He looked at himself, at Korree, in wonder.