The tunnel was very narrow, a mere crack in the wall, and Robin was hard put to squeeze through in a couple of spots. But it was not too long and, in a few minutes, Robin felt from the change in air and echo that it had opened out into a wider area.
Peter's flash confirmed this. They were in a small air-pocket bubble several yards wide. They crossed this while Peter searched along the floor. He stopped, pointed down.
"We go down again, through this hole in the floor. There's a short drop of only a few feet, but be careful."
Peter stepped over to the hole, sat down, and eased himself out of sight. Robin looked down, could see the floor of another cave just below. He dropped his pack through and squeezed down.
Here they were in a sort of shallow flaw running lengthwise, and they had to walk in a crouched position to keep their heads from bumping the low ceiling.
Robin wondered how Peter knew which way to go, but looking carefully, he realized that his brother was only following the trail of his footsteps made on arriving—for there was a thin coating of dust on this floor that showed the trail.
"How did you ever find this passage?" asked Robin, his voice echoing flat and high in the passage.
"Saw the sealed cleft top running across the bottom of this crater. Found a spot near it where some sort of gas was hissing out. Went down it, and simply followed every lead that pointed in the direction of the cleft." Robin knew that behind this reply undoubtedly lay a lot of sweat and agony. Peter had made the trip carrying an unconscious body with him!
The low passage ended in a small cave-bubble. A break at the top of this was the next line of direction. Peter had simply dropped down on his arrival, but they waited to catch their breath. They would have to jump for it.
"Do you suppose Von Borck is following us?" asked Robin while waiting.