Tunnels 01, Tunnels

look at this...," Chester replied, his voice a little shaky.
    At the center of the grotto, in the deepest part of the clouded pool that lay there, stood the remains of a massive machine of some description. The boys' flashlights revealed ranks of large red-brown cogwheels that were still held together within what remained of a shattered cast-iron frame so tall that in places the stalactites growing from the rock ceiling above touched it. It was as if a locomotive had been mercilessly disemboweled and then left there to die.
    "What the heck is it?" Chester asked as Will stood silently beside him, examining the scene.
    "Beats me," Will answered. "And there are bits of metal all over the place. Look!"
    He was shining his flashlight around the margins of the water, following them as far as he could into the deepest reaches of the cavern. Will's first thought had been that the banks were streaked with minerals or something similar, but on closer inspection he discovered they were littered with more bolts like the one he'd just found, all with chunky hexagonal heads. In addition to these, there were spindles and countless pieces of jagged cast-iron shrapnel. The red oxide from these intermingled with darker, inky streaks, which, from their appearance, Will took to be oil spills.
    As they stood there in amazed silence and surveyed this worthless treasure trove, they became aware of a faint scratching sound.
    "Did you hear that?" Chester whispered as they trained their lights in the direction of the sound.
    Will moved a little farther into the cavern, treading carefully on the uneven floor, now invisible beneath the water.
    "What was it?" gasped Chester.
    "Shh!" Will stopped and they both listened, peering around.
    A sudden movement and a small splash made them jump. Then a sleek white object leaped from the rippling water and streaked along one of the metal members, stopping still on the top of a huge gearwheel. It was a large rat with a glistening, perfectly white coat and big, bright pink ears. It wiped its snout with its paws and flicked its head, spraying droplets into the air. Then it reared up on its hind legs, its whiskers twitching and vibrating in their flashlight beams as it sniffed the air.
    "Look! It doesn't have any eyes," Will hissed excitedly.
    Chester shuddered in response. Sure enough, where there should have been eyes there was not even the tiniest break in the sleek, snowy fur.
    "Yuck, that's disgusting!" Chester exclaimed as he took a step back.
    "Adaptive evolution," Will replied.
    "I don't care what it is!"
    The animal twitched and arched its head in the direction of Chester's voice. Then, the next instant, it was gone, diving into the water and swimming to the opposite bank, where it scurried away.
    "Great! He's probably gone to get his friends," Chester said. "This place will be swimming with them in a minute."
    Will laughed. "It's only a stupid rat!"
    "That was no normal rat -- whoever heard of eyeless rats?"
    "Come on, you big baby. Don't you remember the Three Blind Mice?" Will said with a wry grin as they began to move around the crescent bank, playing their beams into the nooks and crannies in the walls and up to the ceiling above them. Chester was stepping apprehensively between the rocks and iron debris, constantly peering behind him for an imagined army of sightless rats. "I hate this," he grumbled.
    As they approached the shadows at the far end of the grotto, Will increased his pace. Chester did likewise, determined not to be left behind.
    "Whoa!" Will stopped in his tracks, Chester bumping into him. "Just look at that!"
    Set into the rock was a door.
    Will's flashlight flicked over its dull, scarred surface -- it looked ancient but substantial, with rivet heads like halves of golf balls spaced around its frame and three massive handles down one side. He reached forward to touch it.
    "Hey! No!" Chester fretted.
    But Will paid him no heed and tapped lightly on the door with his knuckles. "It's metal," he said, running his palm over the surface -- shiny, black, and uneven, like burned molasses.
    "So what? You're not thinking of going in there, are you?"
    Will turned to him, his hand resting on the door. "This is the only way my dad could've gone. Dead straight I am!"
    With that he reached up, grasped the topmost handle, and tried to pull down on it. It refused to budge. He thrust his flashlight at Chester and then, using both hands, tried again, heaving down with all his weight. Nothing