Tunnels 01, Tunnels

of vision. He watched, fascinated, until it dawned on him that something was not quite right. At the same time a dull ache gripped his chest, and a clammy sweat broke out on his temples.
    One two, one two, one... one... one two...
    He slowed his pace, feeling the resistance as he drew breath. It was peculiar; he couldn't quite put his finger on what was wrong. At first he thought it was simply exhaustion, but no, it was more than that. It was as if the air, having lain undisturbed in these deep tunnels, maybe ever since prehistoric times, was behaving like a sluggish fluid.
    One two, one...
    Will came to an abrupt halt, loosening his collar and massaging his shoulders under the straps of his backpack. He had an almost irresistible urge to throw the weight off his back -- it made him feel constricted and uneasy. And the walls of the passage bothered him -- they were too close, they were smothering him. He backed away into the middle of the tunnel, where he leaned on his knees and took in several gulps of air. After a while, he felt a little better and forced himself to straighten up.
    "What's wrong?" Cal asked, eyeing him worriedly through the glass slit of his mask.
    "Nothing," Will replied as he fumbled in his pocket for the map. He didn't want to admit to any weakness, certainly not to his brother. "I... I just need to check our position."
    He'd taken it upon himself to navigate their route through the many twists and turns, aware that a single mistake would lose them in this subterranean maze of such extraordinary complexity. He remembered how Tam had referred to it as the "Labyrinth" and likened it to pumice stone with innumerable interlocking pores worming randomly through it. At the time, Will hadn't thought much about his uncle's words, but he now knew precisely what he'd meant. The sheer scale of the area was daunting, and although they had been making good time as they were moving rapidly through the passages, Will figured they had a long way yet to go. They were helped considerably by a gentle downward gradient, but this in itself caused him some consternation; he was only too aware that every foot they descended now would have to be climbed again before they reached the surface.
    He glanced from the map to the walls. They had a pinkish hue to them, probably due to the presence of iron deposits, which could explain why his compass was worse than useless down here. The needle dithered lazily around the dial, never settling in the same position long enough to give any sort of reading.
    As Will looked around him, he reflected that the passages could have been formed by gas trapped under a solidified plug of some kind, as it tried to escape through the still-molten volcanic rock. Yes, that could be the reason there weren't any vertical tunnels. Or possibly they'd been formed by water exploiting lines of weakness in the millennia after the rock cooled. I wonder what Dad would make of this , he thought before he could stop himself, his face falling as he realized that he'd probably never see his father again. Not now.
    And try as he might, he couldn't stop remembering that last glimpse of Chester as he'd rolled helplessly across the floor, straight back into the clutches of the Styx. Will had let him down yet again...
    And Rebecca! There it was, incontrovertible, he'd seen it with his own eyes. She was a Styx. Despite the fact that he felt so weak, Will's blood boiled. He wanted to laugh out loud as he thought back to how worried he'd been about her.
    But there was no time to reflect now -- if he and Cal were going to get through this alive, he had to make sure they didn't stray off course. He took one last glance at the map and refolded it before they resumed their journey.
    One two, one two, one, one, one two.
    As their feet cruched in the fine red sand, Will longed for a change, a landmark, anything to break the monotony, to confirm that they were still on the right track. He began to despair that they were ever going to reach the end. For all he knew, they could be going around in circles.
    He was thrilled when they eventually came across what looked like a small headstone, with a flat face and a rounded top, set against the passage wall. With Cal looking on, he crouched down to brush the sand from its surface.
    A sweep of his hand revealed a symbol carved into the pink rock about halfway down the face. It was comprised of three diverging lines, which fanned out like rising rays or the prongs of a trident.