Tunnels 03, Freefall

this.
    "Yes, but this is naturally occurring -- it must be flowing out of the strata. One theory is that it's derived from huge accretions of primordial microscopic organisms which, over the centuries, bacteria breaks down to leave to just this fraction." Dr. Burrows wiped his fingers on his trousers. "By the way, try not to get too much on your skin -- it's not unknown to have arsenic and other nasties in it."
    "Bit late for that," Will muttered, examining his hands as they set off again.

    * * * * *

    After what seemed like several days of hauling themselves through the ever more abundant vegetation and further deposits of bitumen, they were finally out of the crater and on level ground again.
    "Incredible!" Dr. Burrows cried. "We're here!"
    "Wherever that is," Will said under his breath. "I thought we'd never reach the top." He stretched his back, enjoying being able to stand up again.
    Dr. Burrows slipped off his Bergen. "Don't think I'll be needing this. Not in this climate," he said, as he removed his duffle coat. He took out his binoculars. "Just look at this place!" he exclaimed. "It's beautiful."
    Screwing up his eyes, Will began to scrutinize the range of hills that formed the horizon whichever direction he turned, and then he examined the deep red soil underfoot.
    Elliott staggered a few paces, and raised her hand to shield herself from the fiery ball of light in the sky. "It's scorching," she puffed.
    "That's because the sun is always directly overhead," Dr. Burrows informed her. "Here it's always midday."
    "What are you talking about?" Will spat.
    Dr. Burrows studied his compass, then looked up. "The Earth doesn't orbit around this sun -- this second sun is up there in the sky day in, day out... in fact, there is only day... there's no night at all here."
    "Only day," Elliott echoed, meeting Will's eyes.
    If what Dr. Burrows was saying was right, Will realized how strange this concept must be for her. Her whole life had been spent underground and all she'd known up to this point was the permanent shade of subterranean lands. Talk about going from one extreme to the other.
    "The Garden of the Second Sun," Dr. Burrows proclaimed as he continued to survey their surroundings. "I shall call it RogerBurrowsLand!"
    At this point, it all became too much for Will. "Dad, I'm sorry but I'm not buying this second sun stuff," he said, shaking his head. He thrust his finger at the scene before them. "Look at the woodland, or forest, or whatever it is over there on the sides of the hills." He shrugged. "All perfectly normal. How can you say we're inside the planet when it all appears so normal? And tell me something -- if you're right, why can't I see the land curve upwards ?"
    "Well, even if those hills weren't blocking our view," Dr. Burrows explained patiently, "the massive scale of this second world, combined with the heat haze, would probably make it difficult for us to see very far. But maybe, given favorable microclimatic conditions, we will be able to observe a little more of the other sides of the sphere."
    Will shook his head again. "So that big burning thing in the sky is what exactly?"
    "I told you -- it's the second sun. It must have been here from the beginning of time, when our planet was created after the Big Bang. And here it's been all that time, without any of us knowing it, spinning away in its own secret existence.
    "You're saying it's like some sort of star?" Will ventured, frowning.
    "Yes. A cloaked star. I suspect it might not be an isolated case, and there are others out there in the universe, but of course we have no way of seeing them," Dr. Burrows suggested. "And common sense dictates that it's far smaller than the sun in the middle of our solar system -- it has to be in order to fit inside our planet."
    "Oh, come on," Will shot back quickly. "Somehow, and I don't know how, we've managed to climb up another of the pores -- one that's open at the top -- and we're on the surface again. I know the plants are a bit weird..." he hesitated as his gaze fell on a large blue flower the size of a beach ball, "but maybe we've come up in Africa or something. Listen to those crickets -- don't you get them in Africa?"
    Nobody spoke as they listened to the rhythmic clicking sounds coming from all over.
    "Cicadas," Dr. Burrows decided. "They sound like cicadas, which you get in tropical areas like--"
    "Told you," Will interrupted him. "We're back on the surface."
    "Really?" Dr. Burrows said. "If that's so,